enterics - flashcards

enterobacteriaceae

* cause primary GI infections
* opportunistic: sepsis, pneumonia, meningitis, UTI
* responsible for many community-acquired and nosocomial infections

cardinal rules for enterobacteriaceae

* GNRs
* ferment glucose
* nitrate to nitrite reduction
* oxidase neg (except plesiomonas)
* all motile (except shig, kleb, yersinia)
* facultative anaerobe
* large, spready, moist, gray, cream colonies

MAC

* lactose, CV and bile salts
* LF = pink
* NLF = colorless

EMB

* lactose, sucrose, eosin Y, methylene blue
* LF = green metallic sheen, blue back
* NLF = colorless

HE

* lactose, sucrose, salicin, bile salts, sodium thiosulfate
* LF = salmon
* NLF = green/blue

XLD

* lactose, sucrose, xylose, bile salts, sodium thiosulfate
* LF = yellow
* NLF = colorless

enterobacteriaceae virulence factors

* adherence: easy colonization
* toxins: food poisoning
* invasive enzymes: spreading factors
* serology

enterobacteriaceae antimicrobial resistance

* ESBLs
* CRE: R to imipenem, meropenem, doripenem, ertapenem OR CPE
* CPE: k. pneumonia (KPC); MBL carbapenemases; NDM

carbapenem resistance

* automated methods, E-test, kirby bauer
* CLSI breakpoints
* ertapenem testing good for CPE
* detection: infection control
* modified hodge test, carbaNP test, neo rapid CARB test

serology

* H Ag: heat stable, flagellar (motility)
* O Ag: heat stable somatic in cell wall (LPS)
* K Ag: heat labile, capsular
* K1 (e. coli), Vi (salmonella)

e. coli characteristics

* beta hemolysis
* LF
* motile sex pili, fimbriae
* H, O, K Ags
* colon biota

e. coli biochemicals

* ferm: glucose, lactose, trehalose, xylose
* indole pos
* MR pos, VP neg
* neg H2S, DNase, urease, PAD, citrate
* IMVC pos pos neg neg

uropathogenic e. coli

* UTIs
* pili: attachment so urine flow doesn’t wash it out
* cytolysins: kill immune cells/stops phagocytosis
* aerobactin: allows bacteria chelate iron

enteropathogenic (EPEC)

* infantile diarrhea children; nurseries and day cares
* adhesin
* malaise, low grade fever, vomiting, diarrhea with mucus

enterotoxigenic (ETEC)

* ==traveler’s diarrhea== requires large inoculum
* watery diarrhea, abd cramps, nausea
* contam food/drink
* colonize small intestine via fimbriae
* releases toxins:
* heat labile (LT): acts on adenyl cyclase so ATP = cAMP = hypersecretion fluids = diarrhea
* heat stable (ST): guanylate cyclase inc cGMP = hypersecretion

enteroinvasive (EIEC)

* adults/children
* dysentery with direct penetration, invasion, destruction of intestinal mucosa
* similar to shigella but needs higher inoculum (non motile NLF)
* watery diarrhea with scant stool, pus, mucus, blood

enterohemorrhagic (EHEC)

* shiga toxin producing
* O157 H7 associated with ==HUS==
* low plts, HA, kidney failure
* watery progressing to bloody diarrhea no pus
* fatal in young kids/elderly
* undercooked meats, unpasteurized milk, apple cider, bean sprouts, spinach

EHEC toxins

* verotoxin I: phage mediated cytotoxin aka shiga toxin (Stx)
* damages vero cells (african green monkey kidney cells)
* neutralized by shiga toxin Abs
* verotoxin II
* neutralized by shiga toxin Abs

how to diagnose EHEC

* stool culture on differential media
* serotyping
* O157 H7 on SMAC plate
* shiga toxin in stool
* 4x or greater in STEC Ab titer

SMAC plate

* MAC containing sorbitol
* O157 H7 does not ferment sorbitol = colorless
* send for serotyping if neg
* other e. coli = pink

MUG test

* tests ability to produce beta-glucuronidase
* breaks down MUG = 4-methylumbelliferone
* fluoresces blue in long wave UV
* rapid ID non EHEC strains
* EHEC do not produce enzyme
* send for serotyping if neg

enteroadherent (EAEC)

* diarrhea and UTIs
* adheres to surface of small intestine via fimbriae
* water diarrhea, dehydration, vomiting, occ abd pain
* lasts 2+ wks
* commensals from colon with special adherence = UTIs
* culture with Hep2 cells = aggregative pattern stacked brick

septicemia and meningitis from e. coli

* meningitis common in neonates/young children
* infected just before/during delivery or with amniotic fluid
* capsule Ag K1: predisposition for meningitis
* bacteremia in adults from UTI or GI source

CLSI - e. coli

* presumptive: oxidase neg, indole pos, GNR
* additional tests for definitive ID
* beta hemolytic, lactose pos/PYR neg OR
* MUG pos
* additional notes:
* isolate must be large colonies and not from GI specimen

kleb, enterobacter, serratia, hafnia characteristics

* opportunistic/nosocomial infections (pneumonia, UTI, wounds)
* citrate pos
* neg H2S, phenylalanine deaminase, indole
* MR neg VP pos
* IMVC: neg neg pos pos

klebsiella characteristics

* non motile
* LF
* mucoid
* pneumonia, oxytoca, ozaenae

k. pneumoniae

* most common isolate
* LRT in hospital pts, UTIs, bacteremia, wounds
* moist gray mucoid
* polysaccharide capsule prevents phagocytosis
* KPC is concern from plasmid transfer

k. oxytoca

* similar to k. pneumoniae but ==indole pos==
* affects similar sites

k. ozanae

* isolated from nasal secretions/cerebal abscesses
* plasmid mediated ESBLs contribute to resistant seen in nosocomial infections

enterobacter (cloacae and aerogenes)

* MR neg VP pos
* motile
* citrate pos
* usually produce ornithine decarboxylase
* lysine decarboxylase not in e. cloacae
* infections in wounds, urine, blood, CSF

pantoea agglomerans

* formerly enterobacter
* yellow

cronobacter sakazakii

* formerly enterobacter
* yellow
* meningitis/bacteremia from powdered infant formula

serratia spp

* ONPG pos (SLF)
* DNase pos
* highly resistant to antimicrobials
* adorifera = dirty, musty odor
* rubidaea = red at RT

s. marcescens

* most clinically relevant
* red pigment
* nosocomia UTI, resp infections
* bacteremic outbreaks in nurseries, cardiac surgery, burn units

hafnia alvei

* delayed citrate rxn
* environmental and human samples
* gastroenteritis isolated from stool cultures

proteus spp

* isolated from urine, wounds, ear, blood infections
* swarmers on non selective media
* burnt chocolate odor
* pos H2S, NLF, PAD, urease

p. mirabilis

* indole neg
* ornithine decarboxylase pos
* if amp “R”
* maltose neg
* penneri = ornithine neg, maltose pos

p. vulgaris

* indole pos
* ornithine decarboxylase neg
* ferments sucrose (Y/Y TSI)

morganella morganii

* UTIs and possible diarrhea
* motile
* citrate neg
* PAD pos

providencia spp

* rettgeri: UTI, nosocomial outbreaks
* stuartii: nosocomial burn unit outbreaks and isolated in urine cultures
* highly resistant to antimicrobials
* citrate pos

edwardsiella tarda

* bacteremia and wound infections
* urea neg
* lysine decarboxylase pos
* H2S pos
* indole pos
* citrate neg

citrobacter spp

* freundii: most common
* nosocomial UTIs, pneumonias, endocarditis rare, intraabd abscesses
* koseri: nursery outbreaks of neonatal meningitis, brain abscesses

citrobacter biochemicals

* weak urease
* LF
* citrate pos
* MR pos
* H2S pos

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* resembles salm on media but neg lysine decarboxylase (salm pos)

lab diagnosis of enterobacteriaceae

* specimen collection/transport
* isolation/ID (sterile vs non sterile)
* full ID on stools
* stools
* looking for NLFs
* XLD, GN, HE, CIN, SS, SMAC
* serology for salm/shig