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Gram Positive Bacteria
Catalase Positive: Staphylococcus
58
Microbiology
Graduate
03/26/2011

Additional Microbiology Flashcards

 


 

Cards

Term

causes 80% suppurative infections

 

2nd leading cause of nosocomial infections

Definition
Staphylococcus Aureus
Term
staphylococcus aureus colonization (prevalence)
Definition

community: 20-50%

 

healthcare workers: 90%

 

higher in hemodialysis patients

Term
predominant site(s) of staphylococcus aureus colonization
Definition

#1: anterior nares

 

others: skin, vagina, axilla, perineum, & oropharynx

Term
most staphylococcus aureus infections result from:
Definition
own strains
Term

common transmission of staphylococcus aureus

(epidemiology)

Definition

from hands of healthcare provider

 

patient to patient (hospital setting)

 

not seasonal (except warm seasons' prevalence for food poisoning)

 

community: major cause of soft tissue infection

Term
3 Staphylococcus aureus virulence factors
Definition

1. structural

 

2. enzymes

 

3. toxins

Term
staphylococcus aureus virulence factors (structural-4)
Definition

1. capsule (inhibit chemotaxis/phagocytosis; adheres to foreign bodies)

 

2. peptidoglycan (inhibit phagocytosis; endotoxin-like)

 

3. teichoic acid (major component of cell wall; mediates attachment to mucosal surface; regulate cationic conc @ cell mem; bind Fn)

 

4. protein A (bind IgG-Fc frag; inhibit opsonization/complement activation)

Term
Ig bound to protein A elicits...
Definition
cell-mediated response => pus formation AND necrosis
Term
Quorum sensing - Staphylococcus aureus virulence factor
Definition

bacteria makes genetic changes due to changes in growth density (different growth phases)

*S. Aureus is a classic example 

 

during initial part of infection, S. aureus growth density is low: bacteria doesn't need to produce toxins, it needs to produce cell surface proteins (ie. Protein A) to establish a colony

*agr locus of S. aureus regulates many of its cell surface proteins (RNA molecule rather than the usual protein gene-expression-regulator)

 

later on, once the infection is established and the organism needs more room, this feature of the bacteria allows it to produce the toxins against the host => degraded host cells serve as bacterial nutrients (tissue damage/disease)

Term
staphylococcus aureus virulence factors (enzymes-5)
Definition

1. coagulase (fibrinogen --> fibrin)

 

2. catalase (detoxify h202)

 

3. hyaluronidase (hydrolyze HAs (major component of host ECM)=spreading factor)

 

4. lipases (hydrolyze lipids in sebaceous areas of host)

 

5. nucleases (digest DNA/RNA=spreading factor)

Term

Staphylococcus aureus virulence factor 

(toxins-4)

Definition

1. alpha/beta/delta/gamma & leukocidins

(toxic for: leukocytes, RBCs, platelets, macrophages, & fibroblasts)

 

2. ETA & ETB = serine proteases (digest anchors holding epidermis to dermis)

 

3. TSST-1 (superantigen; systemic effects)

 

4. enterotoxins (A-E) (superantigens; stim T cells/cytokine release/inflamm med by mast cells; incr intestinal peristalsis/fluid loss/vomiting)

Term
superantigen mechanism (S. aureus virulence)
Definition

activate T cell (binds TCR & MHC II on APC) => no antigen needed

*=> excessive T cell #s (up to 20% of total)

*high cytokine #s (IL-1/TNF/IL-2)

 

=> non-specific immune response (extremely dangerous)

 

 

Term

catalase/superoxide dismutase mechanism

(S. aureus virulence factor)

Definition

SOD: 02+2H-->02+h202

catalase: h202-->h20+02

*s. aureus breaks down the h202 required by PMN myeloperoxidase to generate more toxic ROIs (to use against bacteria)

 

=> pts w/ chronic granulomatous disease vulnerable to s. aureus & NOT streptococcal infection because catalase-negative organisms are susceptible to the host immune system's use of h202 produced through the bacteria's metabolic processes

Term

staph infections caused by MRSA (in the US):

1974

1995

2004

Definition

1974: 2%

1995: 22%

2004: 63%

Term
2 types of staphylococcus aureus caused disease
Definition

1. invasive (cutaneous and non-cutaneous) 

-organism is located w/in the affected areas

 

2. toxigenic

-disease caused by bacterial toxins

Term
Impetigo
Definition

Bacterial cause: (S. aureus: 80%; S. pyogenes OR mixed: 20%) invasive & cutaneous disease

 

limited to epidermis

 

acute & contagious

 

common in children (face & limb) AND during summer/tropical climates

 

progression:small macule (small discolored spot on skin) --> pustule on erythematous base --> pustule ruptures & is replaced by honey brown crusting

Term
folliculitis
Definition

most common cause: S. aureus (invasive & cutaneous)

 

superficial & pyogenic infection of hair follicles

 

reduced risk: w/ good skin hygiene

 

 

Term
furuncle
Definition

most common cause: S. aureus (invasive & cutaneous)

 

boil: several hair follicles & adjacent tissues are affected

 

reduced risk: w/ good skin hygiene

Term
hordeolum/style
Definition

most common cause: S. aureus (invasive & cutaneous)

 

folliculitis of eyelid

 

erythematous or pustular appearance

Term
carbuncle
Definition

S. aureus disease: (invasive & cutaneous)

 

coalesced furuncles (more serious disease); extended to deeper subcutaneous tissue (multiple sinus tracts)

 

common locations: nape of neck, upper back, or buttocks

 

progression: tight/erythematic skin --> effaces & releases pus

 

associated symptoms: chills & fever

 

 

Term
wound infections
Definition

most commonly colonized by gram negative organisms

 

most common gram positive organism: staphylococcus aureus (invasive & cutaneous disease)

 

occurs after surgery/trauma

 

presentation: edema, erythema, pain, accumulation of purulent material

Term
mastitis
Definition

s. aureus intro into ductal system through cracked nipples (invasive & cutaneous disease)

 

presentation: tenderness, fever, fatigue, possibly aggressive, may require drainage

Term
bacteremia
Definition

when s. aureus (invasive & non-cutaneous disease) is the cause

 

> 50% acquired after surgery OR from contaminated IV catheter

 

usually from innocuous-appearing skin infections

Term
endocarditis
Definition

when s. aureus is the cause (invasive & non-cutaneous disease)

*does NOT require any pre-existing damage to heart tissues (as would endocarditis from other causes)

 

life threatening (50% mortality)

 

incr freq of embolization of friable vegetations (=> erythematous lesions in periphery)

Term
staphylococcal pneumonia
Definition

prevalence: 2% of community pneumonia (*PV leukocidins important role here); 20% nosocomial-pneumonia (15-40% fatality <= those who develop are already ill)

 

cause: aspiration of oral secretions OR hematogenous spread

 

presentation: tissue destruction, massive hemoptysis, septic shock (all due to toxins)

 

remember: streptococcus pneumoniae is the most common cause of bacterial pneumonia

Term
osteomyelitis
Definition

most common cause: s. aureus (invasive & non-cutaneous disease)

 

cause: hematogenous spread OR extension from subcutaneous infection

 

children: in metaphyseal areas of long bones (from low flow areas => time for bacteria to get out of the circulation)

 

adults: vertebra (rarely in long bones)

 

presentation: sudden onset of localized pain AND high fever

Term
septic arthritis
Definition

most common cause in most individuals:

s. aureus (however, N. gonorrhoeae (gram-negative coccus) is most common among the sexually active)

 

presentation: pain w/ mvmt, erythematous/swollen joints, pus in aspirated fluid

 

common location(s): knee (50% of cases), wrists, ankles, & hips

Term
Scalded Skin Syndrome (Ritter's disease)
Definition

caused by: exfoliative toxins A & B (s. aureus-toxigenic disease) break desmoglein-1 (polypeptide) in desmosome (connect adjacent skin cells)

*stratum granulosum is susceptible be/c it lacks the Dsg-3 (polypeptide) that usually compensates for ETA/ETB hydrolysis of Dsg-1 in other strata

 

presentation/progression: abrupt onset of perioral erythema (covers entire body in 2 d) --> large bullae/cutaneous blisters (like burns) --> desquamation (in 5-7 d) --> blisters (2 wks) & positive nikolsky's sign

 

*blisters do NOT contain organism

 

 

Term
positive nikolsky's sign
Definition
pressure displaces the skin
Term
bullous impetigo
Definition

localized SSSS

 

infection, NOT toxigenic => bacteria will be present w/in blister fluid

 

presentation: erythema does not extend beyond blister borders

Term
toxic shock syndrome
Definition

cause: enterotoxin or enterotoxin-like TSST-1

*in menstruation-associated TSS cases: >90% caused by TSST-1

 

mechanism: TSST-1 strains multiply in hyper-absorbant tampons 

 

presentation: abrupt (fever, hT, whole-body-erythematous rash); multiple organs involved; entire skin desquamates (2-3 wks); markedly red tongue

 

fatality: previously high, currently 5%

Term
food poisoning
Definition

most common cause of food borne illness: staphylococcus aureus (50% strains produce 8 distinct enterotoxins)

*heat stable (produced by bact in food @ RT, stable in re-heating)

 

superantigen mechanism? (not well understood)

 

presentation: severe vomiting (w/in 3-4 hrs)

*toxin w/in vomitus (bacteria absent)

 

therapy: fluid replacement NOT antibiotic (be/c this in an intoxication NOT an infection)

Term
antibiotic associated enterocolitis
Definition

most common cause: Clostridium difficile 

2nd: staphylococcus aureus (produce ETA & leukotoxin E/D)

 

presentation: watery diarrhea, abdominal cramps, fever, inflammation of intestinal mucous membrane (bacteria present in stool)

 

increased risk: w/ use of broad spectrum antibiotics

 

 

Term

s. aureus ID

 

abscess (scrape the base)

Definition

fewer organisms in pus

 

gram stains: gram positive cocci

Term

s. aureus ID

 

bacteremia 

Definition

good: culturing blood

 

bad: staining blood (so few organisms)

Term

s. aureus ID

 

ssss

Definition

good: look at nasopharyngeal sample

 

bad: looking at blister fluid (usually not here!)

Term

s. aureus id

 

bullous impetigo

Definition
:) looking in blister fluid (bacteria found here!)
Term

s. aureus id

 

tss

Definition

check vaginal samples, bacteria will be there

 

bacteria will NOT be in blood :(

Term

s aureus id

 

food poisoning

Definition

:) bacteria in food/toxin in vomitus

 

:( bacteria NOT in feces/vomitus

Term

s aureus id

 

blood agar

Definition
hemolytic and golden yellow colonies
Term

s aureus id

 

tellurite-glycine agar

Definition

positive: s aureus changes color --> black

 

glycine inhibits growth of species OTHER than staph

 

differential due to tellurite reduction to tellurium

Term

staphylococcus epidermidis 

 

"CNS" or "CONS"

Definition
Coagulase Negative Staphylococcus
Term

staphylococcus epidermidis virulence factors

 (3)

Definition

1. NO protein A, alpha-toxin, or coagulase (s epidermidis is often drug resistant)

 

2. teichoic acid (glycerol teichoic acid & glucosyl residues)

 

3. slime (facilitate adherence to catheters; forms protective biofilm; interferes w/ PMN phagocytosis)

Term

What organism is this?

 

gram positive coccus

 

coagulase positive

 

catalase positive

 

grape-like clusters

 

tellurite-glycine/mannitol-salt agar positive

 

blood agar: golden-yellow colonies exhibiting hemolysis

Definition
staphylococcus aureus
Term
staphylococcus epidermidis diseases (2)
Definition

1. major cause of infections associated w/ intravascular devices (ie. prosthetic heart valves, shunts, etc.); also in prosthetic joints, large wounds, and catheter induced UTIs

 

2. high incidence in hospital setting (contaminates pt care equipment/environmental surf w/ biofilm)

Term
prosthetic valve endocarditis
Definition

due to s. epidermidis (high mortality rate ~60%)

 

location of vegetations: prosthesis-tissue junction @ sewing ring (bacteria cannot grow on inert material of the prostheses)

 

complications: sepsis, embolization, congestive heart failure, cardiac rupture, etc.

Term
staphylococcus epidermidis identification
Definition

gram positive coccus

 

catalase positive

 

coagulase negative

 

blood agar: white non-hemolytic colonies

 

mannitol-salt/tellurite-glycine agar negative

Term
staphylococcus saprophyticus virulence factor
Definition

not known

 

can colonize periurethral skin & mucosa

Term
staphylococcus saprophyticus diseases
Definition

cystitis (inflammed bladder)

pyelonephritis

*commonly present w/ dysuria and/or pyuria

 

bacterial UTI in sexually active women (7-20%)

*E. coli the most common cause

 

side note: commonly drug resistant

Term
identify staphylococcus saprophyticus
Definition

NOVOBIOCIN-RESISTANT

 

gram positive coccus

 

blood agar: white colonies

 

catalase positive

 

coagulase negative

 

mannitol-salt agar test negative (cannot ferment mannitol)

Term

other staphylococci (2)

 

and their associated diseases

Definition

staphylococcus haemolyticus

 

staphylococcus capitis

 

endocarditis, UTIs, wound infections, opportunistic infections

Term
[image]
Definition
staphylococcus saprophyticus is noboviocin resistant
Term
[image]
Definition

osteomyelitis

 

acute form most commonly caused by staphylococcus aureus

Term
[image]
Definition

septic arthritis

 

most common cause, generally: staphylococcus aureus

most common cause, among sexually active: neisseria gonorrhoeae

Term
[image]
Definition

catalase positive: staphylococcus species

 

catalase negative: streptococcus & enterococcus species

Term
[image]
Definition

mannitol salt agar

 

growth selective for staphylococcus <= high salt

test differential for S. aureus <= mannitol fermentation indicated by color change (positive result = orange/yellow)

Term
[image]
Definition

tellurite-glycine agar

 

growth selective for staphylococcus <= normal flora growth inhibited by glycine

 

test differential for S. aureus <= tellurite reduction to tellurium (indicated by color change: positive result = black)

Term
[image]
Definition

coagulase test (ONLY staphylococcus aureus is coagulase+)

 

positive result: w/ incubation in plasma, S. aureus => coagulation

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