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Microbiology
Gram-negative rods:Enterobacteriaceae
Part IIKaren Honeycutt, M.Ed., MT(ASCP)SM
CLS 418 Clinical Microbiology I
Student Laboratory Session
Microbiology
Enterobacteriaceae AntigensGNR: Enterobacteriaceae
• “O” – somatic, part of cell wall (serogroup)– Stimulates earliest antibody
• “K” – capsular, heat labile (serotype)– “Vi” (virulence) specific Salmonella typhi “K” antigen
• “H” – flagellar, heat labile (serotype)– Latest antibodies formed
• Use specific antisera to identify organisms beyond “species” level
• Example: Escherichia coli O157:H7
Microbiology
Escherichia coliGNR: Enterobacteriaceae
• Most common facultative organism in stool– Colony counts to determine fecal
contamination of water
• E.coli “inert group” (Alkalescens-Dispar)– Very inert– Nonmotile– Can be biochemically mistaken for a Shigella
(a stool pathogen)
Microbiology
Escherichia coliGNR: Enterobacteriaceae
Colony morphology
BAP: beta-hemolytic
EMB: green metallic sheen
MAC: dark pink diffuses around
colony
Microbiology
Escherichia coliGNR: Enterobacteriaceae
• #1 etiologic agent of UTI
• Meningitis in 0-3 month age group
Microbiology
Escherichia coliGNR: Enterobacteriaceae
• Enterohemorrhagic E. coli O157:H7– Ingest contaminated food (undercooked
hamburger, unpastuerized apple juice & milk, leaf lettuce)
– Bloody diarrhea– Children especially susceptible to HUS– Specific screening agar: SMAC, MacConkey
agar with sorbitol (not lactose)• E. coli O157:H7 is sorbitol neg (clear on
SMAC)
Microbiology
Escherichia coli
GNR: Enterobacteriaceae
• Gastroenteritis – 4 distinct syndromes caused by 4 distinct E. coli strains
• Usually not diagnosed by culture
Microbiology
Escherichia coli - Identification
GNR: Enterobacteriaceae
• Beta-hemolytic • EMB: Green metallic sheen
MacConkey Agar Indole CitrateKIA
Microbiology
Shigella sp. – Disease State
GNR: Enterobacteriaceae
• Overt or primary pathogen (never NF)
• Bacillary dysentery or shigellosis
• Only human to human transfer
• 4 subgroups (A, B, C, D)
• Shigella sonnei (subgroup D) most common in US and least severe disease
Microbiology
Shigella sp. – Identification
GNR: Enterobacteriaceae
MacConkey
KIA
Always nonmotile!
LIALDC (-) & LDA (-)
Microbiology
Shigella sp. – Identification
GNR: Enterobacteriaceae
• Biochemical identification should be confirmed with serogrouping
• Reportable disease
Microbiology
Citrobacter sp.
GNR: Enterobacteriaceae
• Opportunistic
• Lactose variable
• LDC & LDA (-)
•C. fruendii: H2S +/-[LDC & LDA (-), H2S +]
LIALDC (-) & LDA (-)
Microbiology
Salmonella sp.
GNR: Enterobacteriaceae
• Overt or primary pathogen (not NF)• Gastroenteritis: mild to fatal (dehydration)
– Ingestion of contaminated food, water, milk• Chicken, eggs
– Contact with infected animals• Reptiles
– Human to human transfer
• Usually doesn’t invade bloodstream
Microbiology
Salmonella typhi
GNR: Enterobacteriaceae
• Overt or primary pathogen (not NF)
• Typhoid fever
• Transmission: human to human
• Specimens: blood, urine then stool
Microbiology
Salmonella sp. Identification
GNR: Enterobacteriaceae
MacConkey
LDC+ H2S +
Glucose “F” H2S +
KIA LIA
Microbiology
Klebsiella sp.
• Opportunistic pathogens
• Klebsiella pneumoniae: destructive pneumonia
• Muciod colony due to capsule
• Always nonmotile!
GNR: Enterobacteriaceae
Microbiology
Klebsiella sp.- Identification
GNR: Enterobacteriaceae
• Muciod colony due to capsule
• Always nonmotile!
KIA LDC+
Microbiology
Enterobacter sp.
GNR: Enterobacteriaceae
• Opportunistic pathogen• Muciod colony due to capsule• ODC+
KIA
Microbiology
Serratia sp.
GNR: Enterobacteriaceae
• Opportunistic pathogen
• Serratia marcescens– Hospitals– Can produce a red
pigment!!– Lactose nonfermenter– LDC +
KIA LIA
LDC+
Microbiology
Proteus sp.
GNR: Enterobacteriaceae
• Opportunistic pathogen• Swarms on BAP, CHOC• Strong urea hydrolyzer: creates alkaline pH in
urine, causes renal calculi
Microbiology
Proteus sp. - Identification
GNR: Enterobacteriaceae
MacConkeyGlucose “F”
H2S +LDA+ & H2S +
++
KIA LIA Urea
Microbiology
Providencia sp. & Morganella sp.
GNR: Enterobacteriaceae
• Opportunistic pathogens
• LDA+
MacConkey
LDA+
LIAKIA
Microbiology
Summary - Enterobacteriaceae
GNR: Enterobacteriaceae
• GNR, Glucose “F”, oxidase “-”, N03 to NO2
• MacConkey growth: LF & NLF
• Normal flora, colonize hospital patients, opportunistic or primary/overt pathogens