SF095

Strict aerobes

Facultative anaerobes

Strict anaerobes

Colonization resistance

Strict aerobes - grow only in the presence of oxygen

Facultative anaerobes - grow in both the presence or absence of oxygen

Strict anaerobes - only grow in the absence of oxygen

Colonization Resistance: myriad of factors including

• Intact skin and mucus membranes
• Competition for nutrients and living space
• Production of biocins (antimicrobial substances) that inhibit other organisms

SF095

“opportunistic” pathogens

How do these differ from differ from “primary” bacterial pathogens

These are normal human microbiota that ususally do not cause damage to the person they colonize, under certain circumstances that allow them to access body sites that are usually sterile, these “normal microbiota” microorganisms can cause severe damage

These may be found as residents (permanently carried without causing disease), or whose presence invariably represents infection and disease.  Opportunistic pathogens generally enter the sterile tissues if defenses are impaired; primary pathogens can infect an immunocompetent person even when defenses are intact.

SF095

Fibronectin

Normally found on human cells facilitates colonization by generally avirulent Gram-positive bacteria which comprise the majority of the normal microbiota in all normally colonized body sites except the colon.  When fibronectin is diminished or absent, then more invasive Gram-negative bacteria can colonize all the normally colonized sites.  Fibronectin depletion occurs in people who are ill, stressed by hospitalization, old, etc.  This explains the common finding of generally saprophytic Gram-negative bacilli belonging to the two ubiquitous families Enterobacteriaceae and Pseudomonadaceae being reported from all sorts of specimens.

SF095

The major groups of normal microbiota of the skin, upper respiratory tract, mouth, gastrointestinal tract and genital tract (Table - in red = most common)

SF095

Discuss the processes that disturb the resident microbial organisms and the consequences of these alterations

The main process is the use of antibiotics.  As well as killing the bacteria that is being targeted, the antibiotics will be killing off many bacteria that are a part of the normal flora.

There will be overgrowth with organisms that normally wouldn’t be found in the area or overgrowth with normal flora organisms that can now proliferate to much greater numbers due to a lack of competition (ex. Clostridium difficile, Candidiasis)

Ex Pseudomembranous colitis (PMC) is an example of this when C. difficile overgrows in the colon and leads to severe diarrhea.

SF095

4 strategies to correct the illness and to reconstitute the normal microbiota

Do the Turoial for SF095 2 cases

1. Stop the antibiotic treatment and hope that the normal flora is reconstituted and forces out the opportunistic infection.
2. Stop the antibiotic treatment and start a new one which is aimed to kill the opportunistic infection.
3. Introduce pro-biotics (“good bacteria”), Lactobacilli for example (in yogurt), to try and over-run and force out the other microbes.
4. Fecal aenema (as a very last resort) – Introduce stool from a healthy individual into the patient so that normal microbes can get reintroduced into the colon and force out the infection.

SF089

Comparison table for Bacteria, Viruses, Fungi and Protozoa

SF089

4 Sterile Sites

1. Internal organs
2. Blood
3. CNS
4. Bladder

SF089

Common Bacterial Shapes

SF089

Gram Stain Table

SF089

Gram Negative lipid bilayer

SF089

Bacterial Growth Graph Characs (4 stages)

Types of DNA transfer in Bacteria (3)

1. Lag phase (close to zero)
2. Exponential Phase (Steep up)
3. Stationary Phase (Plateau)
4. Decline

1. Conjugation - Cell to cell transmission of Chromosomal or Plasmid DNA

2. Transduction - Virus (phage) transfer of most types of DNA

3. Transformation - Naked DNA uptake (from surroundings)

SF089

Actions of Antibiotics

1. Inhibit cell wall synthesis (Ex. Penicillin)
2. Inhibition of Pr. Synthesis (erythromycin, streptomycin)
3. Injury to Plasma Memb (Polymyxin B.)
4. Inhibition of Enz. Activity by antimetabolites (trimethoprim)

SF089

Selective Toxicity

Broad Spectrum Antibiotics

Bactericidal vs. Bacteriostatic

Selective Toxicity:  An antibiotic should selectively act on the pathogen and not on the human cell.  Selective toxicity is often expressed as the therapeutic index or therapeutic ratio or therapeutic window. The therapeutic index is the ratio of the toxic dose to the therapeutic dose
Higher is better

Broad Spectrum: Defines antibiotics that act against different kinds of pathogens (eg. gram-positives, gram-negatives, typical bacteria, atypical bacteria, aerobes, anaerobes).  Antibiotics may also be classified as antibacterial, antifungal, antiviral and antiparasitic.

Bactericidal: refers to the ability of an antibiotic to kill an organism (≥ 3 log10 reduction in original inoculum over 24 hours. This effect is often concentration dependent, species specific and media or biological fluid dependent.

Bacteriostatic: refers to reversibly inhibiting growth (reduce < 3 log10 over 24 hours), if the agent is removed the organism regrows

SF089

 Minimum Inhibitory Concentration (MIC)

Minimum bactericidal concentration (MBC)

Minimum Inhibitory Concentration (MIC) represents the activity of an antibiotic.  The MIC is the lowest concentration of an antibiotic that prevents growth of the pathogen.

The MBC (minimum bactericidal concentration) is the lowest concentration that kills (≥ 3 log reduction in original inoculum over 24 hours) the organism

A bactericidal agent demonstrates a MBC/MIC of 2-4
A bacteriostatic agent displays a very high MBC/MIC ratio (if it kills at all)

SF089

Antimicrobial Susceptibility Testing

Dilution: Serial dilutions of the antibiotic are made in a liquid medium which is inoculated with a standardized number of organisms and incubated for a prescribed time. The lowest concentration (highest dilution) of antibiotic preventing appearance of turbidity is considered to be the minimal inhibitory concentration (MIC). At this dilution the antibiotic is bacteriostatic.

Disk Diffusion is a test which uses antibiotic-impregnated wafers to test whether particular bacteria are susceptible to specific antibiotics. A known quantity of bacteria are grown on agar plates in the presence of thin wafers containing relevant antibiotics. If the bacteria are susceptible to a particular antibiotic, an area of clearing surrounds the wafer where bacteria are not capable of growing (called a zone of inhibition).

SF089

Classifications of Rigid Thick Walled Cells - Extracellular

Classifications of Rigid Thick Walled Cells - Intracellular

Classifications of Flexible Thin Celled Walls

Wall-less Cells

Gram Positive - Cocci, Spore Forming (Bacilli), Non-Spore Forming Bacilli

Gram Negative - Cocci, Rods - Facultative, Rods - (Aerobic, and Anaerobic), Acid-Fast Bacilli

Gram Negative - Obligate Intracellular Parasites

Ex Chlamydophila, Rickettsia (Rocky Mountain Spotted Fever)

Spirochetes - Troponema (Syphilis), Borrelia (Lyme Disease)

(Wall-less) = Mycoplasma (Pneumonia)

SF089

Differentiating between gram positive and negative

Cell wall
Gram-negative have a thin peptidoglycan layer Gram-positive have a thick peptidoglycan layer

Outer membrane

Gram-negative bacteria contain LPS (lipopolysaccharide) (endotoxin)

Gram-positive have no outer membrane

Either pink/red which is called Gram negative, or blue-black/purple which is Gram positive

Staining Process:
Step 1: Stain with Crystal Violet (Both Purple)
Step 2: Stain with Gram’s Iodine (Both Purple)
Step 3: Add a decolouriser (Gram Negative loses stain)
Step 4: Add Safranin Red (Gram Negative Stains Red, Gram Positive Stains Purple)

SF089

Additional info notes sheet

SF102

3 crucial elements necessary for the development of any infectious disease

1. Microbial pathogenicity and the ‘weapons’ = virulence factors that contribute to microbial damage
2. Interactions between the human and the pathogen
3. Human susceptibility and defenses

SF102

Interactions between the human and the pathogen involve one or more of the following 4:

• Features of microbes which enhance colonization
• Pili or fimbriae, slime layers (biofilm or glycocalyx), capsules, capsids.
• Substances which damage cells and tissue directly
• exotoxins, proteolytic enzymes.
• Features of microbes which help them evade body defenses
• pili, capsules, IgA protease, intracellular parasitism, intracellular survival, molecular mimicry, antigenic variation (drifts and shifts), M-protein, protein-A.
• Damage produced by over-expression of the immune response
• superantigens, endotoxins.

SF102

Virulence

Avirulent

Some factors that contribute to the pathogenicity and virulence of infectious agents (6)

Describes the degree to which an organism is pathogenic

Describes an organism that is incapable, in a normal immunocompetent person, of causing disease

Virulence Factors:

1. Ability to adhere and grow in our tissues (Pili/fimbriae, capsules, tissue tropism, receptors)
2. Production of various substances which inhibit our defense mechanisms or which interfere with normal cell functions (enzymes, toxins).
3. Special surface structures which make it difficult for our phagocytes to engulf and destroy the infectious agents (capsules, slime or biofilm).
4. Ability to change itself and "hide" from our immune system (antigenic variation/mimicry).
5. Ability to enter a phagocyte and prevent intracellular killing (facultative intracellular parasite).
6. Ability to trigger an overpowering immune response with lethal outcomes (superantigen).

 Note: Resistance to antimicrobials is not considered to be a ‘classic’ virulence factor

SF102

2 mechanisms by which microorganisms may produce cell/tissue damage and cause disease...

1. Toxin production:

Exotoxins are polypeptides produced by bacteria and can lead to tissue damage or activation of “pumps” and “channels”. Exotoxins can be produced by some Gram-
positive and Gram-negative bacteria. Endotoxin=lipopolysaccharide (LPS) is produced only by Gram negative bacteria and is not usually released from viable bacterial cells. It is classically released upon death and disintegration of these bacteria (usually, 1 counter example). Both peptidoglycan and endotoxin may lead to the signs of systemic inflammatory response syndrome (SIRS), sepsis and septic shock.

2. Invasion and inflammation:

Bacteria and other microbes must usually enter the body via a portal of entry and then attach to their receptors (tissue tropism) before they can grow and multiply (colonize) and cause damage. 

SF102

Certain enzymes that virulent microbes release can lead to...

Capsules, M-protein and protein-A are important...

Type of inflammatory response in which macrophages and T-lymphocytes predominate...

local tissue injury whereas other enzymes facilitate spread of the organism into contiguous tissues, the lymph and/or the blood. Proteolytic enzymes may also allow bacteria to withstand phagocytes (both ingestion and digestion). 

antiphagocytic factors that trigger a pyogenic (pus cell=PMN=polymorphonuclear neutrophil) response while at the same time hampering phagocytosis.  These antiphagocytic virulence factors, in combination or not with proteolytic enzymes, contribute to the pathology seen in acute pyogenic infections.

This is called granulomatous inflammation.  No enzymes or toxins seem to be involved but bacterial, viral, fungal, etc. antigens stimulate cell mediated immunity (CMI) and granulomas form in which most of the eliciting microbes are killed but some may survive.

SF102

Toxin Production by Microbes (2 types)

• Exotoxins are produced by either Gram-positive or Gram-negative bacteria and are released into the environment by the bacteria.
  
  
• Endotoxin is part of the bacterial cell wall and is not usually released into the environment by the bacteria (except blebbing of endotoxin by live Neisseria meningitidis)
• Most endotoxins= lipopolysaccharide (LPS) - can lead to the clinical symptoms associated with sepsis.
• The term “endotoxin” is meant to indicate a heat-stable, cell-bound polysaccharide-like toxin to contrast and differentiate this type of toxin from heat-labile protein toxins found in culture filtrate outside the cells, specifically exotoxins. 
• Heat-stable endotoxic properties of LPS are largely due to the glycopeptide portion called “lipid A". 
• Endotoxic properties include:
• fever production (pyrogenicity),
• lethality
• tissue necrosis activity
• complement activation
• B-cell mitogenicity
• immuno-adjuvant activity
• antitumor activity.

SF102

The major structural components of the cell wall of

Enterobacteriaceae

• inner cytoplasmic membrane
• middle peptidoglycan layer
• exterior membrane consisting of two layers
• inner phospholipid protein layer
• outer LPS layer

The LPS is composed of three regions:

• O-specific polysaccharide chain (region 1-most exterior moiety)
• Serologic specificity (uniqueness)
• Core polysaccharide (region 2-central moiety)
• shows much less variability than the O-specific chain and is often identical in large groups of Gram-negative bacteria
• Lipid A-moiety (region 3-inserted into the peptidoglycan)
• Toxicity, most conserved part, not all produce the same intensity of FX (septic shock specifically fever, hypotension and disseminated intravascular coagulation (DIC))
  

wwf

SF102

Comparison table for endo and exotoxins

SF102

Comparsion table of certain exotoxins:
Diphtheria, Tetanus, Botulinum, Pertussis

SF102

Non-specific Resistance to Infection

• Normal indigenous microflora
• Resident flora
• Transient flora
• Genetic factors
• Natural antibodies
• Morphologic integrity
• Normal excretory secretions and flow
• Cellular activity
• Phagocytosis
• Natural killer cells
• Fibronectin
• Antibody response (B-Cells)

SF102

Generally: How do Pathogens Overcome Host Defenses? (4 ways)

Superantigens

1. Adherence
2. Capsule
3. Enzymes
4. Toxins

Superantigens are responsible for cross-linking of the class II major histocompatibility MHC (proteins) and the T-cell receptor of the antigen presenting cell (APC) leading to unregulated release of interleukins which contribute to streptococcal toxic shock syndrome

Ex. Streptococcus pyogenes

SF102

Responses to Toxins

• If exposed to exotoxins:
• Antibodies against the toxin (antitoxins)
• Inactivated exotoxins (heat, formalin or phenol):
• No longer cause disease, but stimulate the production of antitoxin
• Altered exotoxins - Toxoids
• Toxoids:
• Injected to stimulate the production of antitoxins and provide immunity

SF097 - Group Tutorial

SF088

Inflammation Definition

Steps in the inflammatory process

A host response to eliminate altered cells, foreign bodies, microorganisms, and antigens.  It is a reaction of the microcirculation characterized by the movement of fluid and cells from the blood into the extravascular compartment

Initiation - recognition that injury has occurred
Amplification - humoral and cellular mediators
Termination - elimination of the “stimulus” and role of “inhibitors” of inflammatory mediators

SF088

The Vascular Response: Changes in the microcirculation and structure of the vessel wall lead to...

1) Vasodilatation
2) Increased blood flow to affected area
3) Loss of endothelial integrity
4) Leakage of fluid and plasma proteins into the extravascular space
5) Emigration of WBC (and RBC) from blood into tissue

SF088

Contrast Between Acute and Chronic Inflammation

Depends on:

persistence of the stimulus and nature of the response

Acute:

- stereotypic
- accumulation of fluid and protein
- activation of platelets
- accumulation of neutrophils

Chronic:

- presence of lymphocytes, macrophages, plasma cells, granulation tissue and fibrosis

SF088

Formation of Extracellular Fluid (ECF): Starling’s forces
(Diagram)

SF088

 Non-inflammatory Edema (w/ ex)

Inflammatory Edema (w/ phases)

Non-Inflammatory Edema:

Caused when the formation of ECF exceeds clearance by lymphatics

Examples:
(1) Pulmonary edema in CHF
(2) Swelling of limb due to venous thrombosis
(3) Diffuse edema due to decrease in COP (e.g., nephrotic syndrome, burn)
(3) Lymphedema due to obstruction of lymphatics

Inflammatory Edema:
Caused by changes in the microcirculation

Phases:
1) Transient vasoconstriction of arterioles (neurogenic)
2) Vasodilatation of precapillary arterioles
3) Increase in permeability of endothelium of the post capillary venule causing leakage of fluid and proteins to ECF (edema)

SF088

2 Mechanisms of Increased Vascular Permeability

Define:

Effusion

Transudate

Exudate

1) Contraction of endothelial cells causing formation of intercellular gaps
2) Direct injury to endothelium

Effusion: Excess fluid in cavity

Transudate: ECF with low protein content

Exudate: ECF with high protein content (e.g. fluid in a blister)

SF088

Define:

Serous exudate

Serosanguinous

Fibrinous exudate

Purulent exudate

Suppurative exudate

Serous exudate: Inflammatory exudate without a prominent cellular response

Serosanguinous: Serous exudate rich in red cells

Fibrinous exudate: Inflammatory exudate with large amount of fibrin

Purulent exudate: Inflammatory exudate rich in cellular response

Suppurative exudate: Inflammatory exudate with liquefactive necrosis of tissue (i.e., pus formation)

SF088

Mediators Released from Mast cells,
Basophils and Platelets

Histamine and Serotonin

From Mast Cells and Basophils:

His/Ser release is activated by:

Ag binding to IgE bound to cell membrane
Anaphylotoxins (C5a, C3a)
Physical (cold)

From Platelets:

His/Ser release is activated by:

Contact with fibrillary collagen
Contact with thrombin

SF088

Arachidonic Acid Metabolites and their Roles in Inflammation

Phospholipids -> Arachadonic Acid -> 5-HPETE (Enzyme 5-Lipoxygenase) or Prostoglandin (Cycloxygenase)

5-HPETE -> Leukotrines -> Vasoconstriction, Bronchospasm, Increased Permeability

Prostoglandin -> Prostacyclin PGI2 (PGD2 etc.)-> Vasodilation, inhibits platelet aggregation

Prostoglandin -> Thromboxane -> Vasoconstriction, promotes platelet aggregation

SF088

Four major enzyme (protein) cascades

1. Complement Cascade (Both Classic and Alternate Pathways)

Most Important Mediators:

• C3a, C5a, C4a (anaphylotoxins) mediate increased vascular permeability by releasing histamine from mast cells
• C5a can activate lipoxygenase pathway in neutrophils and monocytes
• C5a is chemitactic for neutrophils, monocytes, eosinophils and basophils
• C3b opsonize bacteria and promotes phagocytosis by neutrophils and macrophages 

2. Coagulation

3. Kinin/kallikrein

Converts kininogen -> bradykinin
Bradykinin inc. vascular permeability and causes pain
Converts plasminogen -> plasmin

4. Fibrinolytic system

Degrades Fibrin -> fibrin split products (FSP)
FSP inc. vascular permeability
Activates complement (C3a -> C3b)

SF088

Hageman Factor (Factor XII)

2 Regulatory Functions of Endothelial Cells

Activation promotes generation of vasoactive mediators from 1,2 and 3 of last card (Coagulation, Kinin/kallikrein, Fibrinolytic system)

1) Secretion of mediators affecting tissue perfusion:

vasodilators - PGI2, Nitric Oxide

vasoconstrictors - Endothelin

2) Regulation of coagulation:

LPS, IL-1, TNF-alpha (increase endothelial secretion of procoagulant factor promoting thrombosis)

SF088

Interrelationships Between the Four Plasma Mediator  Systems Activated by Factor XII

SF088

Nitric Oxide Roles in Inflammation (5)

• Vascular smooth muscle relaxation
• Decreased platelet aggregation and adhesion
• Decreased leukocyte recruitment (compensatory regulation
• Interaction with O2- to form antimicrobial metabolites (OONO-, nitrosothiols)
• Mitigates potential inflammatory damage to host cells and tissues

SF088

Cellular Recruitment sequence of responses:

What are the first cells recruited?

Cellular Adhesion Molecules (Def'n)

Sequence of responses:
1) Margination
2) Adherence
3) Emigration
4) Chemotaxis

Neutrophils: First cells recruited by mediators called chemotactic factors

Cellular Adhesion Molecules: Endothelial cell membrane glycoproteins that enhance the adhesion and migration of leukocytes across the vessel wall

SF088

Regulation of Leukocyte Recruitment: Chemotaxis

• Directed cell migration in direction of increasing [ ] of chemotactic factors
• C5a important
  Examples:
• Bacterial and mitochondrial products (N-formylated peptides such as FMLP)
• Chemokines [IL-8 (C-X-C) and MCP-1 (C-C)
• Products of arachidonic acid metabolism especially LTB4
• Cytokines (interleukins, colony stimulating growth factors, TNF-alpha and interferons)

SF088

Phagocytosis sequence of events (3)

Leukocyte Bactericidal Activity: O2 dependant

Leukocyte Bactericidal Activity: Non-O2 dependant

Cells Involved: Neutrophils and macrophages
Sequence of events:
1) Recognition (opsonization, Ig and C3b)
2) Internalization
3) Digestion

O2 dependant:

Superoxide (O2-),  H2O2, Hypochlorous acid (HOCl) and  Hydroxyl Radicals (OH)

Note: Congenital deficiencies in this system cause recurrent, severe bacterial infections

Non-oxidative (O2-independent):
- Lysozomal hydrolases
- Bacterial permeability increasing protein
- Defensins
- Lactoferrin (Fe chelator)
- Lysozyme (degrades cell wall of Gram+ bacteria)
- Major basic protein (MBP) and eosinophil cationic protein (cytolytic for parasites)

SF088

Key Biochemical Events in Leukocyte Activation

Key events:
1)Receptor-ligand binding
2)Phospholipase-C activation
3)Inc intracellular Ca²⁺
4)Activation of protein kinase C
5)Resulting biological activities

- chemotaxis
- modulation of adhesion molecules
- elaboration of arachidonic acid metabolites
- secretion/degranulation
- oxidative burst

SF088

Tissue Injury Caused by Inflammatory Response: Mechanisms (3)

Clinical Examples

Mechanisms:

1. Extracellular release of lysosomal enzymes and O2- during phagocytosis
2. Reverse endocytosis
3. Damage to endothelial cells inactivation of anti-proteases such as alpha1-antitrypsin

Clinical Examples of Leukocyte-induced Injury:

1. Acute respiratory distress syndrome
2. Acute transplant rejection
3. Glomerulonephritis
4. Reperfusion injury
5. Septic Shock
6. Vasculitis

SF088

Systemic Manifestations of Inflammation

Fever:
- Role of endogenous pyrogens (IL-1, TNF-alpha)
- Inc. prostaglandin synthesis in thermoregulatory centers of the hypothalamus

Leukocytosis:
- Increase in neutrophil count in blood (bacterial infections)
- Stimulated by CSF from macrophages and T cells
- Release of immature neutrophils (“shift to the left”) into blood
- Viral infections - lymphocytosis
- Parasitic infestations and allergic reactions -> Inc eosinophils

Acute Phase Response:

1. fever
2. leukocytosis
3. anorexia
4. altered sleep patterns
5. inc acute phase proteins

Acute Phase Proteins:
Synthesized by liver
Stimulated by IL-6 (macrophages, fibroblasts,
epithelial cells)
Cause inc in ESR

SF088

Pivotal Role of Macrophages (Diagram)

SF088

Outcome after Inflammation

1. Return to normal vascular permeability
2. Drainage of edema fluid and protein into lymphatics
3. Pinocytosis of edema fluid and protein by macrophages
4. Phagocytosis of apoptotic neutrophils by macrophages
5. Phagocytosis of necrotic tissue debris by macrophages
6. Disposal of macrophages

SF173

Medically important Streptococci (4 types)

1. Streptococcus pyogenes (Gp. A Streptococci) ->lives on skin, only problem with virulent M types (skin soft tissue infections) -> Most imptnt type
2. Streptococcus agalactiae (Gp. B Streptococci)
3. Streptococcus pneumoniae (#1 cause of all upper resp infections)
4. Enterococcus faecalis (in colon, Cause UTIs)

dd

SF173

Streptococcus Shape

Biology (Weapons)

Transmission

Shape: Spheres, in a chain

Weapons:

Catalase negative:

H2O2 (made by neutrophils) --> O2 + H2O
Hemolytic:

(a - hemolysis) – partial hemolysis – S. pneumoniae

(ß - hemolysis) – complete hemolysis – S. pyogenes (GAS)

(y - hemolysis) – non-hemolytic - ? E. faecalis or S. bovis

Transmission:

Most streptococci are actually part of normal flora:

Throat – viridans strep, S. pneumoniae, S. pyogenes

Skin – Group A Strep, Group B Strep (vagina) (must clear pre-birth to prevent transmission)

Intestine – Enterococcus faecalis

Disease is caused by gaining access to tissues or blood (cut on skin etc.)

SF173

GAS (S. pyogenes)

Pathogenesis (3 main types)

Further sub-typed based on the reactivity of the M-protein also located in the cell wall. No M type = Avirunlent.  All (currently over 80) M types cause diseases. M types are:

Rheumatogenic – rheumatic fever or

Nephritogenic - acute glomerulonephritis

Pathogenesis:

Pyogenic inflammation: (pus forming)
Occurs locally at tissue site
        Ex. Pharyngitis, cellulitis

Exotoxin production (toxigenic):
May cause widespread symptoms, with no organism

Scarlet fever - toxin spreads, causes widespread rash
toxic shock syndrome - gets into blood and travels

Immunologic:

Antibody against component of the organism cross reacts and forms immune complexes that damage normal tissue

Rheumatic fever (follows after Pharyngitis)
Acute glomerulonephritis

SF173

Main types of GAS Infections

Streptococcus Colonization vs Disease

a) streptococcal pharyngitis

b) scarlet fever (SF)

c) infectious impetigo

d) erysipelas (type of cellulitis)-> butterfly distrib. on face

e) cellulitis with or without lymphangitis (“blood poisoning”)
d and e characterized by multiplication and lateral spread of S. pyogenes into the deep layers of the skin.

f) streptococcal toxic-shock syndrome

g) necrotizing fasciitis (“flesh-eating disease”) -> toxin spreads fast!

h) post-streptococcal acute rheumatic fever (after pharyngitis) [PS-ARF] [autoimmune complication]

i) post-streptococcal acute glomerulonephritis (post skin infections) [PS-AGN] [autoimmune complication]

Colonization: attachment, growth and multiplication without triggering body defenses. No signs or symptoms

Disease (also called infection): colonization plus body defenses active to try to limit further growth and multiplication which leads to signs and symptoms

SF173

GAS Virulence Properties (6)

1. M-protein – antiphagocytic
   
   
2. lipoteichoic acid (cell wall constituent) – adherence
   
   
3. Exotoxin:
   A is responsible to streptococcal toxic shock syndrome
   B rapidly destroys tissue and in large amounts causes necrotizing fasciitis
   exotoxins are a subgroup of superantigens
   
   
4. Hemolysins: Streptolysin O causes beta-hemolysis on blood agar, antibodies (ASO) develop after group A streptococcal infections. This rise in ASO titre can be used for diagnosis of rheumatic fever.
   
   
5. Hyaluronidase: known as spreading factor because it degrades hyaluronic acid the ground substance of subcutaneous tissue facilitating the rapid spread of S. pyogenes skin infections (cellulitis)
   
   
6. Streptokinase: fibrinolysin, dissolves fibrin in clots, thrombi and emboli

SF173

Prevention of Streptococcal Infections

Rheumatic fever: Treat GAS pharyngitis with penicillin 

Endocarditis: Amoxicillin prophylaxis prior to invasive dental surgery (if damaged heart valves)

Neonatal sepsis due to GBS: Screen women with vaginal culture (35-37 weeks). If culture positive treat with penicillin IV at delivery.

Note: all GAS are susceptible to penicillin

“Strep throat”/ Strep Pharyngitis”: Penicillin or amoxicillin (macrolide if pen-allergic)

SF173

Streptococcus pneumoniae (“Pneumococcus”) - 8 points

1. Streptococcus pneumoniae or “pneumococcus” is a Gram-positive diplococcus that produces alpha-hemolysis on blood agar
   
2. S. pneumoniae can be differentiated from species of viridans group Streptococcus (common cause of endocarditis and also alpha hemolytic), by using a bile solubility test or an optochin disk test (S. pneumoniae are bile soluble and optochin sensitive)
3. S. pneumoniae on Gram stain is "lancet shape“
   
4. It has a polysaccharide capsule that acts as a virulence factor for the organism as is it anti-phagocytic
5. There are >90 different capsular types
6. It is an obligate human pathogen (only humans)
7. S. pneumoniae is the major bacterial cause of upper and lower respiratory infections:
   Otitis media, sinusitis, Bronchitis, pneumonia, Meningitis, sepsis (splenectomy)
8. Treat with Amoxicillin (Also Pneumovax and Prevnar)
   

SF173

Enterococcus faecalis

• Gram-positive cocci that often occur in pairs (diplococci) or short chains
• Enterococci typically exhibit gamma-hemolysis (non-hemolytic) on blood agar
• Classified as Group D Streptococcus with two main species being common commensal (normal microbiota) in the intestines of humans
       E. faecalis (90-95%)
       E. faecium (5-10%)

SF130

Protozoa

Protos (first/primary); zoon (animal)

• Unicellular eukaryotic
• Subkingdom/phylum protozoa
• Subphyla:
• Sarcodina (amoebas)
• Mastigophora (flagellates)
• Ciliophora (ciliates)
• Sporozoa (gametogony/schizogony)
• Microspora (microsporidia)

SF130

Metazoa

Meta (after); zoon (animal)
Complicated multicellular. 2 Phyla.

• Phylum – helminth (helmins – worm)
• Subphyla:
• Nemathelminths (nema – thread)
• Nematodes (roundworms)
• Platyhelminths (platys – broad/flat)
• Trematodes (flukes)
• Cestodes (tapeworms)

and

• Phylum – arthropoda (invert., exo., jointed legs)
• Classes:
• Insecta (six legs, {wings}, separate head/thorax/abdomen)
• flies, mosquitos, bedbugs, fleas, lice
• Arachnida (eight legs, fused head/thorax/ab)
• spiders, scorpions, mites (scabies)

SF130

Definitive Host

Intermediate Host

Gametogony/Sporogony

Schizogony

Definitive Host
–the animal in which a parasite passes its adult existence and/or sexual reproductive phase

Intermediate Host
–the animal in which a parasite progresses through its larval stage or asexual reproduction stage

Gametogony/Sporogony
–reproduction resulting in the union of two gametes (microgamete and macrogamete) to form a zygote; eg. sporozoa, helminths
–sexual reproduction

Schizogony
–reproduction by binary fission; eg. sarcodina, mastigophora, ciliophora, sporozoa, microspora
–asexual reproduction

SF130

Malaria life cycle

SF130

 strongyloides stercoralis

Micro-sized larva penetrate through skin on foot. Travel to lungs, then up trachaea, down esophagus, and into SI. Lays eggs there. 2 types of larva (rabdidiform and phylariform). Phylariform can recycle this life cycle, even for 30 years. Periodically its bursts through colon, then travels back up to lungs, but they drag in bacteria all over body.

Only bad when you are immunocomprimised. Called hyperinfection. Diagnosed with high eisonophil counts. Could notice a moving rash.

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Parasites: Human Health Impact

Malaria

Giardiasis

Cryptosporidiosis

Strongyloidiasis

Hookworms

Pinworms

Schistosomiasis

Ectoparasites

Malaria:

• 2.4 billion in >100 countries at risk, 300-500 million cases annually and ~1 million deaths annually (most <5 y/o)
• 4th leading cause of childhood deaths (10%) in developing countries

Giardiasis:

• common cause of chronic malabsorption diarrhea in North America (“beaver fever”)
• difficult to detect/diagnose

Cryptosporidiosis:

• emerging important cause of diarrhea in North America
• waterborne outbreaks

Strongyloidiasis:

• autoinfection cycle; long-lived infections >40 years
• potentially lethal hyperinfection syndrome in immune compromised (including iatrogenic!)

Hookworms:

• most common cause of Fe def anemia in developing countries
• contributes to severe protein deficiencies

Pinworms:

• relatively innocuous but very common, lay worms on anus, itchy rectum, kids scratch, then re-infect their mouths

Schistosomiasis:

• estimated 500 million people infected in endemic areas
• long asymptomatic phase, leading to severe chronic complications including liver, colon and bladder cancer

Ectoparasites:

• live on/in the skin
• major vectors (ticks, fleas)
• disease causing (lice, scabies, myiasis)

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Parasite Modes of Transmission

and examples

• Penetration intact skin
• soil (Stronglyoides) and water (Shistosomiasis)
• larval penetration (hookworms)
• Ingestion
• soil, water and food
• Blood feeding insects
• arthropod-borne
• Fomites
• clothing, bedding, beds
• Sexual
• ectoparasites (crabs), trichomonads
• anal oral contact (GI parasites)
• Autoinfection
• strongyloidiasis, pinworms
• Bloodborne
• malaria, trypanosomes
• Transplacental
• toxoplasmosis

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Parasites Modes of Pathogenesis (5)

Direct tissue trauma

• skin invasion (scabies, myiasis)
• larval migration through organs (hookworms, flukes)

Enzymatic lytic necrosis

• amebiasis (invasive colitis)
• malaria (rbc’s, hemolysis)
• hookworm (rbc’s, Fe def anemia)

Granulomatous reactions (non-caseating)

• macrophages and epithelioid cells walling off parasite/eggs with multinuclear giant cells (and eosinophils)
• malignant transformation potential
• liver flukes (biliary Ca)
• schistosomiasis (liver, colon, bladder Ca)

Eosinophilia

• invasive helminths (trichinosis, toxocariasis, strongyloidiasis)
• migratory phases (hookworm, ascariasis)
• rarely protozoa (toxoplasmosis, isosporiasis)
• allergic immune response

Allergic reactions

• dermatitis (scabies)
• asthma (ascariasis)
• anaphylaxis (echinococcosis – hydatid cysts)
• urticaria (swimmer’s itch)

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Structure & function of virus components

• Size and shape varies, but very small. Biggest (Pox) can only just be seen by regular microscope.
• Contain either RNA or DNA
• Either Enveloped or non-enveloped
• The lipid envelope consists of human cell membrane with viral proteins inserted
• The lipid layer is fragile (drying, stomach acids damage it & render the virion non-infectious)

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Replicative Steps & Sites Where Influenza Antiviral Drugs Act to Inhibit Virus Replication

How is HIV prevented?

1. Adsorption – random collision leads to binding of virus by ligand to cell surface receptor

This is where most vaccines act - not antivirals

2. Penetration = internalization of virion into cytoplasm
3. Uncoating = release of genome into cell

Drug: Amantadine

4. Transcription = RNA or DNA replication

Drug: Ribavirin

5. Translation = synthesis of proteins
6. Assembly of virion
7. Budding & release = may be lethal (lysis – e.g. HSV) or not (chronic persistent infection – hep B, C)

Drug: Oseltamivir & zanamivir

HIV is stopped at:

1. Reverse transcriptase by AZT like drugs

2. Most important is as stage of cleavage of polyproteins by porteases - drugs are called protease inhibitors

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zoonoses

Droplet Size and Site of Infection

Survival of Influenza A on Surfaces

Infectious diseases of animals

Rabies most commonly from skunks

Large droplets settle fast, and in upper resp tract

Small Droplets settle slowly, and in lower resp tract

Hands: 5 to > 60 minutes
Paper & other porous surfaces: 12 hours
Stainless steel, plastics: 24 – 48 hours

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Mode of transmission of Viruses (5)

Portal of entry (6)

Mode of transmission

1. Direct contact (skin, mucous membranes)
2. Airborne
3. Oroenteric – enteroviruses
4. Direct inoculation

–Rabies in saliva of biting dog

–West Nile virus – mosquito bites

5. Blood borne

Maternal-fetal viremia
e.g. rubella, HIV
Transfusions or IVDU
e.g. HBV, HCV, HIV (CMV, EBV)

Portal of entry

1. Respiratory tract – influenza
2. GI tract – enteroviruses
3. Skin – HPV
4. Genital mucosa – HIV, HSV
5. Blood
6. Placental – rubella

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Family Enterobacteriaceae: E. Coli

• E. coli is a Gram-negative facultatively anaerobic bacilli (2 part cylinder)
  
• Normal microbiota in the large intestine
• The majority of E. coli strains are avirulent, but some have the ability to cause infections such as urinary tract infections (eg. cystitis, pyelonephritis, prostatitis), intra-abdominal infections, bacteremia, sepsis
• Some E. coli (serotype O157:H7) may cause serious food poisoning (hamburger disease)
• E. coli are able to survive for brief periods outside the body making them a good indicator organism to test environmental samples for fecal contamination (drinking water, swimming pools, lakes, etc)

Enterobacteriaceae Family also includes:

Shigella

Salmonella

Klebsiella

Enterobacter

Serratia

Proteus

Yersinia

All of which reside in the large intestine, but E.coli is the most important

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Transmission of E. coli

• fecal-oral transmission with common routes being unhygienic food preparation, farm contamination due to manure spread, irrigation of crops with E. coli contaminated greywater or raw sewage or direct consumption of E. coli -contaminated water
  
  
• Cattle are the primary reservoirs of E. coli O157:H7 as it is normal flora in the rumen and is shed in their feces
  
  
• Food products associated with E. coli outbreaks include raw or undercooked ground beef, vegetables such as sprouts or spinach, unpasteurized apple juice and foods contaminated by infected food workers via fecal-oral route

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E. coli Infections (4 subtypes)

Different “pathotypes” of E. coli cause infectious diseases: These are genetically distinct subgroup of E. coli that has a distinct and characteristic set of virulence determinants, a characteristic epidemiology, and a somewhat unique spectrum of clinical disease

Intra-abdominal infections

When E. coli escape the intestinal tract (eg. as a result of perforation due to an ulcer, a ruptured appendix or surgery) and enter the abdomen, they may cause intra-abdominal infection such as peritonitis which can fatal without prompt treatment

Urinary tract infections (UTIs)

Uropathogenic E. coli (UPEC) is responsible for the vast majority of UTIs

Colonic E. coli colonize the urethra and ascend up the urinary tract to the bladder causing cystitis and potentiallly to the kidneys (causing pyelonephritis) or the prostate in males causing prostatitis

Gastroenteritis

Various E. coli serotype, E. coli O157:H7

Gastroenteritis caused by E. coli is usually associated with eating unwashed vegetables (lettuce, sprouts), drinking unpasteurized apple juice and eating meat contaminated post-slaughter

E. coli O157:H7 is known to cause serious and even life-threatening complications like hemolytic-uremic syndrome (HUS)

Neonatal meningitis

E. coli containing a capsular antigen K1 can colonize the newborn's intestine and lead to bacteremia with resulting neonatal meningitis

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Virulence Factors of E. coli (6)

1. Adhesins:

Surface organelles - fimbriae or pili

Promote adherence of bacteria to mucosal surfaces (colonization)

The P-fimbriae responsible for urinary tract infection, pyelonephritis, and urosepsis

The S-fimbriae associated with neonatal sepsis and meningitis

2. Colinization Factor Antigens (CFA):

Enterotoxigenic E. coli (ETEC) strains responsible for gastroenteritis

3. Capsule:

Promote virulence by decreasing the ability of antibodies to bind to bacteria (antiopsonization) and of white blood cells to phagocytize (antiphagocytic)

Capsules are usually relatively poor immunogens and poor activators of complement

4. Iron Aquisition:

High affinity iron-capturing system

Excrete an iron-chelating compound or siderophore

Hemolysis

5. Plasmids:

Self-replicating non-chromosomal units of DNA R-plasmids (Resistance-plasmids) play a significant role in antimicrobial resistance

6. Toxins

Exotoxins

Hemolysins (RBC, WBC etc)

Enterotoxins

Two major classes:

1. heat-stable toxin (ST)

2. heat-labile toxin (LT) (similar to cholera toxin)

Leads to an increased electrolyte and fluid secretion and inhibition of resorption

Results in increased fluid in the small intestine

Endotoxins:

The toxic portion of lipopolysaccharide (LPS) resides in the lipid A region

Causes fever, leukopenia, thrombocytopenia, disseminated intravascular coagulation (DIC), and activation of the complement (C’) pathways

Other important effects of endotoxin include release of vasoactive substances and direct impact on cardiovascular function

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Bacteremia

Septicemia

SIRS

Sepsis

Severe sepsis

Septic shock

Bacteremia - the presence of bacteria in the blood

Septicemia - the presence of pathogenic organisms in the bloodstream, leading to sepsis

Systemic Inflammatory Response Syndrome (SIRS) [2 or more of the following]

• Temp > 38C or < 36C
• HR > 90 beats/min
• RR > 20 breaths/min
• WBC > 12,000/ul or > 10% bands

Sepsis: SIRS + documented infection

Severe sepsis: Sepsis + organ dysfunction

Septic shock: Sepsis-induced hypotension

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Enteric E. coli (EC) Classification

Enterotoxigenic E. coli (ETEC):
Classified on the basis of serological characteristics and virulence properties:

Classic traveller’s diarrhea

Profuse watery diarrhea that may mimic cholera

Toxins and additional accessory virulence factors make it uniquely capable of producing severe disease and/or large outbreaks

Enterohemorrhagic E. coli (EHEC):
Associated with two syndromes:

Hemorrhagic colitis with abdominal pain and bloody diarrhea
Hemolytic-uremic syndrome (HUS) characterized by

hemolytic anemia, thrombocytopenia and acute renal failure

E. coli O157:H7 have most frequently associates with both, however, several other serotypes have also been associated with this disease

Enteroinvasive E. coli (EIEC)

causes a dysenteric form of diarrheal illness.

Capable of invading and proliferating within epithelial cells of the large intestine, eventually causing death of the cell.  

They do not form enterotoxins, like ETEC

Clinically the illness is characterized by watery diarrhea, often with mucous and leukocytes, a scant bloody stool, severe abdominal cramps and fever.  The symptoms are usually self-limiting

Enteropathogenic E. coli (EPEC)

usually uncomplicated diarrhea

Enteroaggregative E. coli (EAEC)

tends to produce prolonged diarrhea

epidemiology is different from other pathotypes, in that it tends to affect older children and adults

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Treatment of E. coli Infections

Emerging Issues with E. coli Infections

UTIs due to E. coli are commonly treated with:

trimethoprim-sulfamethozaxole (TMP-SMX)

fluoroquinolone (eg. ciprofloxacin or levofloxacin) amoxicillin (if susceptible)

Invasive infections requiring intravenous (IV) treatment are commonly treated with:

IV penicillins (eg. ampicillin, piperacillin/tazobactam)

cephalosporin or

fluoroquinolones

Emerging Issues with E. coli Infections:

Antimicrobial Resistance:

beta-lactam antibiotics - extended-spectrum beta-lactamases (ESBLs)

ESBLs confer resistance to all cephalosporins and are frequently multi-drug resistant (MDR)

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Table of Differential Characteristics of Exotoxins and Endotoxins of E. Coli

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SF113 - E. Coli tutorial

Staphylococci

Look over tutorial

2 medically important genera of Gram-positive cocci:

Staphylococcus and Streptococcus

3 medically important Staphylococci

Staphylococcus aureus* (S. aureus)

Staphylococcus epidermidis

Staphylococcus saprophyticus

Shape is spheres in a grape like cluster

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Staphylococcus aureus

Transmission

Weapons

Normal flora in 10-40% individuals

Nose (anterior nares)

Skin/vagina

Throat

Transmission:

Shedding from human lesions (wound/boil)

Fomite contamination

Weapons:

Catalase positive:

H2O2 (made by neutrophils) --> O2 + H2O
Coagulase positive:

Enzyme causes plasma to clot

Hemolytic (ß hemolysis):

Lyses RBC

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Staphylococcus aureus Infections (3 main types of Inflammatory, 3 main types of Toxigenic)

Inflammatory:

1. Skin Infections

Surgical wound infections

Eyelid infections – blepharitis, stye

Ex. Abscesses, impetigo, furuncles, carbuncles, paronychia, cellulitis, folliculitis

2. Bacteremia and Septicemia

From local lesion, IV drug user or IV catheters

Can seed any organ system but especially heart valves (endocarditis) and bone (osteomyelitis)

3. Pneumonia

post surgery or post viral respiratory infection (eg. post-influenza)

Toxigenic:

1. Food Poisoning

2. Toxic Shock Syndrome (TSS)

3. Staphylococcal Scalded Skin Syndrome (SSSS)

Fever and bullae and large areas of skin slough in sheets classically in babies and young infants

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Staphylococcus aureus Virulence Properties

1. Enzymes (4):

Coagulase: bacteria protect themselves from host defenses by causing localized clotting

Catalase: breakdown H2O2 made by neutrophils

Hyaluronidase: breaks down hyaluronic acids present in the acellular matrix of connective tissue

Beta-lactamases (penicillinases and cephalosporinases) break down lactam antibiotics

2. Toxins (4):

Alpha: the alpha toxin acts on a wide variety of cell membranes (erythrocytes, leukocytes, platelets, fibroblasts) and leads to cell lysis 

Leukocidin: this enzyme damages human phagocytic cells (eg. PVL-Panton Valentine leukocidin) [CA-MRSA]

Enterotoxins: Acts like a superantigen to stimulate large amounts of interleukins Cytokine release from lymphoid cells triggers enteric nervous system to activate vomiting centre in brain

Toxic Shock Syndrome Toxin (TSST): Superantigen that causes toxic shock (5-25% of strains). From wound infections/tampons/nasal packing Toxin enters blood (toxemia)

3. Cell-Components:

Capsule: Anti-phagocytic defense by interfering with opsonization

Protein A: Major protein in cell wall, prevents activation of complement, thus opsonization and phagocytosis reduced

Teichoic Acid: Mediate adherence to mucosal cells and induce septic shock

Slime production

Thick Cell wall

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MMSA and MRSA (Treatment)

Prevention of Staphylococcus aureus Infections

Methicillin-susceptible S. aureus (MSSA)

 - treat with ß-lactam (eg. penicillin or cephalosporin)

Methicillin-resistant S. aureus (MRSA

 - treat with Vancomycin

Infection control: hand washing

Persistent colonizers of the nose: mupirocin

Surgical prophylaxis: cefazolin

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Staphylococcus epidermidis

Pathogensis

 Weapons

Prevention

 Treatment

Normal flora 100% individuals

Colonized on skin/mucous membranes

Generally avirulent (only in opportunistic situations)

Pathogenesis:

Enters bloodstream (bacteremia). Once in blood can metastasize.

Weapons:

Catalase positive
Coagulase negative Does NOT cause plasma to clot Non-hemolytic (gamma hemolysis)

      Does NOT lyse RBC

Prevention:

Good IV line/catheter care

Surgical prophylaxis: Aseptic technique and cafazolin

Treatment: (susceptible to antimicrobials (Amoxicillin))

If methicillin (cloxacillin) susceptible MSSE:

Treat with ß-lactam (eg. penicillin or cephalosporin)

If methicillin (cloxacillin) resistant MRSE:

Treat with Vancomycin

Remove catheters/hardware

SF107

Activity of Penicillins Table

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Activity of Penicillins Table Infromation
“must knows” about the organisms

1. Staph aureus:
Gram positive normal flora
Skin and soft tissue infections

2. Streptococcus pneumonia
Chains or diplocci
Obligate human pathogens
Found in nasopharynx
RESPIRATORY INFECTIONS (#1 cause worldwide): Acute otitis media (AOM), bronchitis, pneumonia, bacteremia, sinusitis

3. Enterococcus (Gram +ve) and E.coli (Gram –ve)
Both live in colon (non pathogenic unless they get out)
E.coli = #1 cause of UTI’s, Enterococcus = UTI’s in elderly

4. Klebsiella
Normal intestinal flora
Part of Enterobacteriacea
#2 cause of UTI in world

5. H.influenza
normal flora in 10% of people (mostly smokers)
Obligate human pathogen
Lives in nasopharynx
RESPIRATORY INFECTIONS (# 2 cause)

6. Pseudomonas
Not normal flora -> ie hospital aquired microbe
Water-bug in hospitals and nursing homes (nosocomial)
Causes pneumonia with 50% mortality

7. B.fragilis
Obligate anaerobe (major one in colon)
In colon  -> the big one in stool 10 000 :1
Doesn’t like to cause infection but causes abscesses in peritoneum

SF107

Activity of Penicillins Table Infromation

Drugs

Penicillin V

• Targets S. pneumonia and Enterococci
• 3 things:
• Strep throat (strep pharyngitis) -> stay on for people with rubella to prevent further infections
• Dental infections
• Syphillis

Cloxacillin

• Targets S.pneumonia and S. aureus
• Just skin and soft tissue infections

Amoxicillin (ampicillin)

• Targets S.pneumonia, Enterococci, H.influenzae and E.coli
• Respiratory infections (sinusitis, bronchitis, AOM)
• Can be taken during pregnancy
• Will use 40% of the time in family practice

Amoxicillin/Clavulanate

• Targets all except Pseudomonas
• Imptnt in:
• Skin infections -> S.aureus, S.pneumonia
• UTI’s -> E.coli
• Intrabdominal Infections -> aerobes and anaerobes, Gram –ve and +ve together: Enterococcus, E.coli, B.fragilis
• Diabetic Foot Ulcers -> Gram –ve’s
• ER drug for animal bites

Piperacillin/ Tazobactam
o    Targets EVERYTHING
o    Use only when you don’t know what’s going on
o    Used in hospital only (IV)

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Activity of Cephalosporins Table

SF107

Activity of Cephalosporins - Drugs

Cefazolin (oral equivalent = cephalexin) - 1st gen

• Targets S.aureus, S.pneumonia, Klebsiella, E.coli, H.influenzae
• Importantly Staph aureus and Strep pneumonia
• Skin and soft tissue infections
• Preoperative Prophylaxis (used in surgery before first incision to prevent entry of organisms into surgery site)

Cefuroxime 2nd gen

• Targets S.aureus, S.pneumonia, Klebsiella, E.coli, H.influenzae
• Importantly Strep. pneumo and H.influenzae = RESPIRATORY INFECTIONS
• 90% pediatric infections, use when Amoxicillin fails

Cefoxitin  2nd gen

• Targets everything Cefuroxime does but also B.frag
• Intra abdominal or genitourinary: aerobes and anaerobes.
• Ex appendicits

Ceftriaxone  3rd gen

• Targets S.aureus, S.pneumonia, Klebsiella, E.coli, H.influenzae
• Covers all Gram –ve Enteriobacteriaceae  infections
• Used only in the hospital (hospital acquired infections)
• Neisseria gonorrhoeae (1 dose), Treponema pallidum and Borrelia burgdorferi

Ceftazidime 3rd gen
o    Covers Pseudomonas aeruginosa
o    Used in hospital

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Other B-Lactam Like Agents (Table)

SF107

Other B-Lactam Like Agents - Drugs

Aztreonam

• Targets E.coli, Klebsiella, H.influenzae, Pseudomonas
• Hospital acquired Gram –ve bacilli infections
• Classified under MONOBACTAMS
• Active against Gram-ve bacilli but not against gram +ve’s and anaerobes
• Treat hospital acquired Gram –ve bacilli infections
• No cross-allergenicity with penicillins

Imipenem (meropenem)

• Target EVERYTHING but MRSA
• Both display cross-allergenicity with penicillins or cephalosporins
• These guys fall under class CARBAPENEMS 
• Used in hospitals for hospital acquired infections and when you have no idea what it is

Vancomycin: (IV only)

• Imptnt that it treats MRSA
• Also, drug of choice with clostridium difficile assoiciated disease (CDAD) - it is a spore former that lives in the hospital - germinate to bacteria in colon
• Side FX: ottotoxicity, Nephrotoxicity

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B-Lactam Hypersensitivity Reactions

Type I (immediate type - anaphylaxis)

occurs in 1 in 10,000-15,000 (mortality 10-25%) within minutes with parenteral and within 2 hours with oral beta-lactams. Manifested by severe broncho-constriction (wheezing), laryngeal edema ± hypotension. Treatment is epinephrine with steroids and supportive care.

Type II (accelerated)

occurs in 1% within 1-72 hours and is manifested by urticaria (hives), fever and rarely, wheezing and hypotension. Mortality is rare.

Type III (delayed)

occurs in 1-10% after 72 hours and is manifested by rashes, fevers, serum sickness, etc. Patients can receive a beta-lactam after having a type III reaction (but you could be sued...your choice)

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Activity of Protein Synthesis Inhibitors Table

Gentamicin

• Treat pilonephritis - gentamicin and ampicillin combo
• Synergism with beta-lactams (like Cloxacillin) can target serious Staphylococcal infections
• Side FX: nephro and ottotoxicity important

Chloram-phenicol

• Treatment of anaerobic infections, meningitis, and severe salmonella infections
• Don’t use in developed countries because can cause aplastic anemia

Clindamycin

• Used for acne, also combined with gentamycin
• Has a bad reputation because it kills B.frag allowing C.diff to grow
• Exam Q: Side effect is Pseudomembranous Colitis, may cause diahrhea, and also a famous cause of CDAD
• Adverse Effects: GI intolerance, Nausea/vomiting with diarrhea

Macrolides = erythromycin, clarithromycin 

Erythro-mycin

• Adverse Effects: ONE OF THE SAFEST DRUGS, but GI problems common, cholestatic Hepatitis is rare and reversible

Clari/Azithro-mycin

• Have greater activity against organisms than Erythromycin
• Respiratory infections (S.pneumonia and S.influenzae)
• Most commonly used on those allergic to penicillin
• Adverse Effects: GI problems less common than Erythromycin, cholestatic Hepatitis is rare and reversible

Tetracycline (Doxycycline)

• Treat Resp infections, Chlamydiae (main treatment), Atypical pneumonia, acne (but must make sure girls don't get pregnant while on the drug)
• Exam Question once again: Contra-indicated in pregnant females and children to age of 8 years old (depress bone growth and cause tooth discoloration) Therefore need to put females on tetracycline on oral contraceptives also.
• Also not to be used in patients with renal or hepatic impairment
• kill flora in vagina -> yeast infections

SF107

Activity of Fluoroquinolones and TMP/SMX Table

SF107

Activity of Fluoroquinolones and TMP/SMX - Drugs

Flouroquinalones = Ciprofloxacin and Levofloxacin/Moxifloxacin

Ciprofloxacin

oral and IV
used for prostatitis and pilonephritis (kidney)

Levofloxacin/Moxifloxacin

• called the resp quinalone
• used for pneumonia, bronchitis, sinusitis
• used when Beta lactams or macrolides won't work
• There may be risks of tendon rupture

TMP/SMX

• sulfinamides
• we can treat MRSA orally with this
• today it is the drug of choice for cystitis
• drug of choice for pneumocystis carnii
• dont use in resp b/c of resistance

SF107

Classes of Antibiotics: Cell Wall Activity

The penicillins, cephalosporins, monobactams and carbapenems are all referred to as beta-lactam antibiotics (beta-lactams) because each has a beta-lactam ring as part of their molecular structure.  All beta-lactams are bactericidal.  They combine with and inactivate penicillin-binding proteins (PBP) responsible for transpeptidation that cross-links the peptidoglycan (murein).  Lack of cross-linking weakens the cell wall and results in cell lysis secondary to high intracellular osmotic pressure.  Vancomycin is a glycopeptide that prevents proper cell wall cross-linking through stearic hindrance and results in cell lysis (bactericidal).

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Antibiotic Resistant Pathogens

1. Staphylococci (MRSA = Methicillin-Resistant Staphylococcus aureus, Cloxixillin-Resistant Staphylococcus aureus in Canada, VRSA)
2. Enterococci (VRE = Vanco resistant enterococci)
3. Gram-Negative Bacilli (ESBL  = Extended spectrum beta-lactamase)
4. C. difficile -> CDAD
5. Yeast (azole-resistant)
6. TB (MDR)

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Community-associated MRSA is in (4)

Causes of Antibiotic Resistance

Community-associated MRSA is in:

1. Injection drug addicts
2. Homeless shelters
3. Nursing homes
4. Native Reserves

Epidemic outbreaks in:

• Day-care centers
• Prison inmates
• Ships; military
• Contact sports

Causes of Antibiotic Resistance:

1. Overuse/abuse of antibiotics in humans
2. Overuse/abuse of antibiotics in non-humans
3. developing countries
4. industry advertising/promoting
5. critically ill patients
6. world travel

SF103

Potential Solutions to Infections Caused By Resistant Superbugs

Probiotics

• Knowledge about resistant infections (www.can-r.ca)
• Infection control (wash those hands!)
• Appropriate antibiotic use
• Vaccination (eg. Influenza and S.pneumoniae)
• If treating a patient:
• Treat as early as possible
• Kill the pathogen
• Discover and develop new antibiotics

Probiotics:

• Definition: live organisms that when administered in adequate amounts confer a health benefit to the host
• Normal, healthy, non-virulent bacteria
• Eg. Lactobacillus spp., Saccharomyces boulardii, Bifidobacterium spp.
• Available as foods, dietary supplements or as pharmaceuticals
• Tested vs untested products (eg. yogurt vs. specific probiotic product)

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How do you test for TB? (4)

Pathogenesis of tuberculosis

1. MAN-2 (skin test): Thrown off if person has had the BCG vaccine. The test only becomes positive 4-6 weeks after infection. a positive test means that the individual has either been exposed, infected, or immunized with the BCG vaccine

2. Sputum test: acid fast stain for mycobacterium.  This is not a definitive test. AFB – Acid fast Bacilli.

3. Culture and Sensitivity: culture is the gold standard for identifying TB.  This takes a few weeks to complete. Sputum should not be held in the mouth to prevent growing oral microbes.

4. Chest X ray: for consolidations and volume loss (i.e. cavities)

Pathogenesis of tuberculosis:

• Preferentially infects macrophages and other reticuloendothelial cells.  Able to replicate within these cells
• Macrophages digest the bacilli and present it on class II MHC molecules to CD4+ cells. 
• CD4+ cells secrete cytokines that attract more lymphocytes and macrophages to the area of infection
• M. tuberculosis is ingested by a macrophage where it is unable to be broken down because it produces an “exported repetitive protein” that prevents it from fusing with a lysosome. 

SF120

BCG is made from...

Tb is treated with...

M Bovis -> attenuated Tb in cows

Treatment for TB is multidrug regimen, generally over a 6 month period.  There are different regimens developed, but most of them are centered on 4 drugs:

rifampin

isoniazid

pyrazinamide

ethambutol

SF128

Primary human fungal pathogens

Dermatophyte genera: Trichophyton, Microsporon, Epidermophyto

• Cause cutaneous infection restricted to the keratin-containing skin structures
• Seen as inflammatory dermatitis with a characteristic (though not always formed) 'ring' lesion

Systemic dimorphic fungal genera: Blastomyces, Coccidioides, Histoplasma

• These are primarily acquired by inhalation of airborne spores released by the environmental growth phase, the filamentous mold phase, composed of hypha and spores.
• Once inhaled into the alveoli of the lungs, the spores grow into their body temperature phase – yeast – most genera have diagnostically pathognomonic morphology in clinical specimens.  This two-phase, temperature-dependent growth morphology is referred to as 'dimorphism' and the fungi are therefore often referred to as dimorphic
  fungi.

However there are also opportunistic infections. The commonest opportunistic mycosis is Candidiasis due to a normally innocuous yeast called Candida albicans which is part of our normal microbiota.

SF128

Antifungal Drugs

• Mainly target the biosynthetic pathways for the unique sterols found in the fungal cytoplasmic membrane – ergosterol and zymosterol
• There are antifungal agents that target DNA synthesis (flucytosine, also known as 5-fluorocytosine), mitosis (griseofulvin) and most recently, glucan in fungal cells walls

SF128

There are two types of fungi...

Differentiate between the various asexual reproductive elements produced by fungi.

Name two fungal diseases which do not involve infection

Yeast and Molds

Yeast grow as single cells and reproduce asexually by budding

Molds grow as long filaments (hyphae) and form a mat (a mycelium).  Some hyphae contain partitions called septa.  Molds reproduce via asexual spores called conidia.

Asexual reproductive elements:

Many fungi reproduce by forming asexual spores (conidia).  The arrangement, the colour and the shape of the spores can help identify the fungi.  Some important types of spore are:

Arthrospores: arise by fragmentation from the ends of hyphae

Chlamydospores: round, thick-walled, and quite resistant (for survival)

Sporangiospores: formed within a sac on a stalk

Yeast produce blastospores, which are formed by budding

Two fungal diseases which do not involve infection:

Mycotoxicosis – caused by ingested fungal toxins
Allergic disease – manifested primarily as an asthmatic reaction

SF106

Empiric Therapy (antibiotics)

Bactericidal VS Bacteriostatic

Therapy initiated on the basis of the clinical diag¬nosis and the urgency of the situation before the results of culture and/or susceptibility are available.

Penicillins, cephalosporins, carbapenems, aminoglycosides, fluoroquinolones,  vancomycin, bacitracin, polymyxins are bactericidal

A bactericidal antibiotic is one that reduces or kills the inoculum by 99.9% (3 log10 decrease in 24 hours).  A bacteriostatic antibiotic is one that inhibits growth (≤3 log10 killing in 24 hours).  The ratio of MBC/MIC for bactericidal agents is usually 2, while for bacteriostatic agents, this ratio is much greater, if these agents kill at all.

Combining bacteriostatic and bactericidal drugs may be more likely to cause antagonism than combining two bacteriostatic or two bactericidal agents

SF106

A general rule of thumb is that the antibiotic concentration should...

Route of antibiotics

exceed the minimum inhibitory concentration (or MIC which is determined in the test tube) by 4-10 times

Bacteria in some sites are pharmacokinetically isolated, that is, the antibiotic has  difficulty in reaching these sites:

Eye (aqueous and vitreous humour)

CSF

Bone

Prostate

In some instances, delivering drug into these sites may require antibiotic administration by special routes.  To effect penetration into abscess walls, pus drainage is imperative.

Routes:

• Oral
• Parenteral
• IV
• Intramuscular
• Special routes = intrathecal, intravitreal, intraperitoneal