Transcript Gram-negative rods: Enterobacteriaceae Part II Karen Honeycutt, M.Ed., MT(ASCP)SM

Gram-negative rods:
Enterobacteriaceae
Part II
Karen Honeycutt, M.Ed., MT(ASCP)SM
CLS 418 Clinical Microbiology I
Student Laboratory Session
Microbiology
GNR: Enterobacteriaceae
Enterobacteriaceae Antigens
• “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
GNR: Enterobacteriaceae
Escherichia coli
• 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
GNR: Enterobacteriaceae
Escherichia coli
Colony morphology
BAP: beta-hemolytic
EMB: green metallic
sheen
Microbiology
MAC: dark pink
diffuses around
colony
GNR: Enterobacteriaceae
Escherichia coli
• #1 etiologic agent of UTI
• Meningitis in 0-3 month age group
Microbiology
GNR: Enterobacteriaceae
Escherichia coli
• 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
GNR: Enterobacteriaceae
Escherichia coli
• Gastroenteritis – 4 distinct syndromes
caused by 4 distinct E. coli strains
• Usually not diagnosed by culture
Microbiology
GNR: Enterobacteriaceae
Escherichia coli - Identification
• Beta-hemolytic
• EMB: Green metallic sheen
MacConkey Agar
Microbiology
KIA
Indole
Citrate
GNR: Enterobacteriaceae
Shigella sp. – Disease State
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•
•
•
•
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
GNR: Enterobacteriaceae
Shigella sp. – Identification
Always nonmotile!
MacConkey
KIA
Microbiology
LIA
LDC (-) & LDA (-)
GNR: Enterobacteriaceae
Shigella sp. – Identification
• Biochemical identification should be
confirmed with serogrouping
• Reportable disease
Microbiology
GNR: Enterobacteriaceae
Citrobacter sp.
• Opportunistic
• Lactose variable
• LDC & LDA (-)
•C. fruendii: H2S +/[LDC & LDA (-), H2S +]
Microbiology
LIA
LDC (-) & LDA (-)
GNR: Enterobacteriaceae
Salmonella sp.
• 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
GNR: Enterobacteriaceae
Salmonella typhi
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•
•
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Overt or primary pathogen (not NF)
Typhoid fever
Transmission: human to human
Specimens: blood, urine then stool
Microbiology
GNR: Enterobacteriaceae
Salmonella sp. Identification
Glucose “F”
H2S +
LDC+
H2S +
MacConkey
KIA
Microbiology
LIA
GNR: Enterobacteriaceae
Klebsiella sp.
• Opportunistic
pathogens
• Klebsiella
pneumoniae:
destructive
pneumonia
• Muciod colony due
to capsule
• Always nonmotile!
Microbiology
GNR: Enterobacteriaceae
Klebsiella sp.- Identification
• Muciod colony due to capsule
• Always nonmotile!
KIA
Microbiology
LDC+
GNR: Enterobacteriaceae
Enterobacter sp.
• Opportunistic pathogen
• Muciod colony due to capsule
• ODC+
KIA
Microbiology
GNR: Enterobacteriaceae
Serratia sp.
• Opportunistic
pathogen
• Serratia marcescens
– Hospitals
– Can produce a red
pigment!!
– Lactose nonfermenter
– LDC +
Microbiology
LDC+
KIA
LIA
GNR: Enterobacteriaceae
Proteus sp.
• Opportunistic pathogen
• Swarms on BAP, CHOC
• Strong urea hydrolyzer: creates alkaline pH in
urine, causes renal calculi
Microbiology
GNR: Enterobacteriaceae
Proteus sp. - Identification
KIA
MacConkey
Microbiology
Glucose “F”
H2S +
LIA
LDA+ &
H2S +
Urea
++
GNR: Enterobacteriaceae
Providencia sp. & Morganella sp.
• Opportunistic pathogens
• LDA+
LDA+
MacConkey
LIA
KIA
Microbiology
GNR: Enterobacteriaceae
Summary - Enterobacteriaceae
• GNR, Glucose “F”, oxidase “-”, N03 to NO2
• MacConkey growth: LF & NLF
• Normal flora, colonize hospital patients,
opportunistic or primary/overt pathogens
Microbiology
GNR: Enterobacteriaceae
Summary - Enterobacteriaceae
• Identification
– Colony morphology: mucoid, swarming,
beta-hemolytic, red pigment
– Lactose fermentation
– H2S +
– Nonmotile
– Deamination (LDA) positive
Microbiology