a foreign microorganism that causes an infection inside your body

-more than 1/4 of all deaths globally

acute respiratory infections

aids

diarrheal diseases - dysentary

TB

Malaria

Measles

Hep B

replicate inside a host and produce large # of progeny and potentially serious infection.

-bacteria, viruses, protozoa, fungi

-can be intracellular (viruses) or extracellular (entamoeba)

-intracellular have access to nutrient, supply genetic material, and can avoid immune response

typically have one infectious stage maturing into a reproducing stage with offspring exiting the host

-arthropods, helminths (worms)

-only extracellular -> feed on host cells or take up nutrients from tissue fluids

-single celled prokaryotes

-have long circular DNA with no envelope found in the nucleoid

-cell wall is complex and often has a thick capsule

peptidoglycan is the main component providing a hydrophilic surface

-elicits innate immune response in humans

Procedure for Gram staining

(important to know)

1. bacteria are heat fixed or dried on a slide

2. stain with crystal violet and gram's iodine

3. excess stain removed by washing w/ acetone-based decolorizer and water

4. red counterstain (safranin) is added

-gram negative bacteria will stain red and gram positive will stain purple

-the extra outer layer of gram negative bacteria serves as a structural barrier for the violet to reach the peptidoglycan layer

-during decolorization, the outer layer is removed, and then gram negatives are stained with counterstain, which is lighter than the original stain

-gram staining doesn't work for:  starved cells, old cells in the stationary phase, cells treated with antibiotics/antibacterials etc., mycobacteria (waxy outer shell)/ mycoplasmas (no peptidoglycan)

-have thick multilayered cell wall made of peptidoglycan surrounding the cell membrane

-peptidoglycan can block phagocytosis and induce fever

-no outer membrane

-lysozyme sensitive

-thicker cell wall

-no lipopolysaccharide

-no production of endotoxin (mainly exotoxins)

-outer membrane is both hydrophilic and hydrophobic due to lipid unique to GN bacteria

-porins (special pores made of protein) allow for passage of nutrition

-lipopolysaccharide on the outer membrane confers antigenic and toxic properties

-lysozyme resistant

-thinner cell wall

-endotoxins releases upon destruction of cell

coccus - spherical (staphylococcus)

diplococcus - two spherical cells together (streptococcus)

bacillus - rod shaped (ecoli)

spiral or spirillum - snakelike (borrelia)

the transfer of genetic material from one bacterium to another via a bacteriophage (bacterial viruses with extrachromosomal genetic elements).

-once in a cell, a transposon can jump between plasmid to plasmid or plasmid to chromosome

1. production of the basic bulding block takes place inside of the cell

2. precursor unit is carried from inside the membrane outside.  The basic units are modified (adding second sugar) and are covalently linked to the preexisting cell wall

-drugs that target this stage require active division of the bacteria

3. a variety of reactions that cross link peptides in the cell wall

prophylaxis - prevantative

empiric - broad spectrum ABs cover many but not all pathogens

definitive - know what pathogen is and tailor therapy to the specific disease state

- cannot make energy or proteins independant of a host cell

- contain RNA or DNA

- have to be able to use host processes to produce proteins, viral mRNA, copies of the genome

- have single stranded or double stranded, linear or circular DNA or RNA within a capsule (capsid)

- virus may only be a nucleocapsid or it may have an outer membrane or envelope

viruses replicate, produce new viruses, and they are released when the cell lyses

the virus is quiescent with the DNA or RNA existing in the host's cytoplasm or in the host's genome

-replication takes place when some type of activation occurs

-biochemical properties: mode of replication

-strucure: size, morphology, nucleic acids

-associated disease

-mode of transmision

-host cell

-target tissue or organ

-multicellular, branching filamentous (hyphae) forms or as unicellular yeast

-distinguished from other eukaryotes by a rigid cell wall made of chitin and glucan and a cell membrane with ergosterol instead of cholesterol

Mycelium- mass of hyphae

superficial- body surface

cutaneous or subcutaneous- nails, subcu skin

systemic- internal organs, systems

opportunistic- cause disease in immunocompromised hosts

reproduction usually asexual; sexual (rare) in an arthropod vector

-common in tropical, subtropical regions

-intracellular parasites- infect erythrocytes, macrophages, brain, muscle, and epithelial cells

-> nutrient uptake from host cells

-extracellular pathogens- infect the blood, intestines, urinary or reproductive tracts -> nutrient uptake from host cells or ingest whole cell

-can continuously change surface antigens

-develop into cyst form under harsh conditions

-consume complement at the cell surface (blocks immune response)

-intracellular protozoans can evade intracellular enzymes

-utilize aerobic and anaerobic respiration

flatworms: tapeworm (cestoda), flukes (trematoda)

roundworms: (nematoda)

-fecal oral route - accidental ingestion of eggs or larvae originating from feces of infected host

-intermediate host - accidental ingestion of larvae in tissue of another host

-active penetration of skin - larval stages invade through skin

-injection by blood-sucking insect - larval stages develop to infectivity in insect

direct: cause disease by feeding on a host

-the bite itself is the "disease"

indirect: transmission of pathogens as they feed

-bite causes another disease

commensalistic- a relationship of convenience

-one benefits, the other is unaffected

mutualistic- a relationship with mutual benefits

-both parties benefit

parasitic- only one party benefits, while one party is adversely affected

1. the microbe must be present in every case of the disease

2. the microbe must be isolated from the diseased host and grown in pure culture

3. the disease must be reproduced when a pure culture is introduced into a non-diseased susceptible host

4. the microbe must be recoverable from an experimentally infected host

viral diseases cannot be cultured

cannot always find an equivalent experimental host

some pathogenic diseases are co-infections

-most common infectious disease.  more than 200 agents cause colds.  spread by nasal/oral transmission and fomites

-rhinoviruses (picornaviridae)cause at least 50%

-coronavirusus (coronaviridae) cause 20%

-incidence decreases with age -> more IgA AB's

-may spread to sinuses, LRT, middle ear

toxic proteins produced by some bacteria (mostly gram positive) and secreted or released after lysis

streptococcal pharyngitis

(strep throat)

Streptococcus pyogenes

-gram positive coccus; facultative anaerobe

-produces many exotoxins (streptolysins -> cause lysis of pharyngeal cells and produce spots)

-cause of 95% of bacterial sore throats

-can spread causing rheumatic fever

cytomegalovirus infection

(CMV) -(pharyngitis)

-largest human herpesvirus (herpesviridae)

-acquired from most bodily secretions and blood

-originally called salivary gland virus- transmitted by salivary glands.  Persistant and latent infections; remains latent in neutrophils, t-cells, and monocytes

-often asymptomatic but can spread to lymphoid tissue, then salivary glands, kidneys, reproductive organs

-dangerous to babies

CMV: enlarges cells that it affects

-infectious mononucleosis (fever, anorexia, lethargy, splenic rupture)

-herpesvirus transmitted in saliva

-replicates in B-cells

-shed in saliva from infected salivary glands and spreads to B-cells in lymphoid tissue

-T-cells proliferate in response to infected B-cells