Microbiology: Gram Negative Bacilli Flashcards Preview

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Flashcards in Microbiology: Gram Negative Bacilli Deck (14):

Commonalities of GN bacilli

-All have LPS virulence factor
-Have 3 different serotypes: O-antigen (cell wall), K-antigen (capsular), H-antigen (flagellar)
-They cannot be ID'd from gram stain, must use culture on selective media, serotyping, and biochemical tests (i.e. presence of beta-galactosidase for utilization of lactose)
-Majority of infection cases
-Sort by site of infection, metabolism (aerobe vs. anaerobe), lactose fermentation, commensal, virulence
-Lactose fermentors: EEK (enterobacter, E coli, Klebsiella)
-Non-lactose fermenters (worse): PPYSS (pseudomonas, proteus, yersinia, salmonella, shigella


Escherichia Coli

-Facultative anaerobe, lactose fermenter, many serotypes (some are commensal)
-Causes food borne illnesses (O157) and neonatal diarrhea (O155 and O111)
-Also causes gastroenteritis, UTI, neonatal meningitis, bacteremia
-6 pathogenic subgroups (all end w/ "EC" for E coli): enterotoxigenic (ETEC), enteroinvasive (EIEC), enteropathogenic (EPEC), enteroaggregtive (EAEC), enterohemorrhagic (EHEC), and diffusely adherent (DAEC)


Virulence factors of E coli

-Adhesins for attachment to epithelia
-Inhibition of immune response by K-Ag
-Toxins of many types



-Many serogroups, not commensal, facultative anaerobe
-S typhi and S paratyphoid are exclusively human pathogens
-Transmitted through contaminated food and water


Pathogenesis of salmonella

-Gastroenteritis by non-typhoid salmonella due to tissue invasion of epithelial lining of large and small bowel
-Penetration of lamina propria causes inflammatory diarrhea
-Typhoid fever caused by S typhi and S paratyphi, which enter circulation through M (phagocytic) cells of the gut (adhesins and invasins allow entry and replication)
-Multiple organs (liver, gall bladder, spleen) can be infected by bacteremia


Virulence factors and Dx of salmonella

-Adhesins and invasins
-Survival after phagocytosis due to catalase and superoxide dismutase
-Acide tolerance response (ART) allows for survival of bacteria in stomach acid
-Dx based on growth on selective media and serotyping


Vibrio cholerae

-Vibrionaceae appear as curved rods (fusiform), w/ single flagellum (motile)
-Can survive high salt levels (halophilic)
-Can be obtained from fecal-contaminated food/water, or from some sea food


Pathogenesis of cholera

-Severe, voluminous, watery diarrhea (rice water), no abdominal pain
-Cholera toxin (phage-borne AC binary toxin) disrupts H2O transport, net efflux
-Has adhesion factors (mucinase), and siderophore (Fe binding protein)
-Dx is culture, with biochemical and serological testing (non-lactose fermenter, oxidase positive



-Obligate aerobe, prototrophic (can use inorganic matter)
-Oxidase positive but does not reduce nitrates
-Ubiquitous, resists disinfection
-Associates w/ nosocomial (hospital-acquired) infections


Pseudomonas aeruginosa

-Obligate aerobe, flagellated, w/ capsule and blue-green pigment
-Produces many nosocomial infections: bronchitis, bronchopneumonia, UTI, bacteremia, endocarditis, complications of burn and surgery wounds
-Can also come from community: complications of cystic fibrosis, ear infections, skin infections (wounds, folliculitis)


Virulence factors and pathogenesis of P aeruginosa

-Adhesin (pili and neuraminidase), flagellum
-Toxins (exotoxin A is similar to diphtheria toxin (inhibits protein synthesis)
-Pigments turn puss green-blue
-Exonzs (elastase, phospholipase, ect)
-Biofilm formation, especially in lungs


Dx of P aeruginosa

-Culture, non-lactose fermenter
-Characteristic blue/green pigment


Haemophilus influenza

-Small pleiomorphic rods, facultative anaerobe
-Commensals: H influenza, H parainfluenza, H ducreyi (STI)
-Disease comes from endogenous bacteria


Pathogenesis of H influenza

-Can cause meningitis (encapsulated)
-Also otitis media, sinusitis, epiglottitis, pneumonia (non encapsulated)
-Virulence associated w/ acquired capsule (serotypes a-f)
-Serotype b is most pathogenic
-Other virulence factors: LPS endotoxin, possibly PRP (polyribitol phosphate, antiphagocytic and acquired), and IgA protease to counter mucosal immunity
-Dx is through typing of X (protophorphyrin) and V (NAD+/NADP+) requirement (only H influenza needs both to survive)