Gram-negative rods: Enterobacteriaceae Part II

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Gram-negative rodsEnterobacteriaceae Part II

• Karen Honeycutt, M.Ed., MT(ASCP)SM
• CLS 418 Clinical Microbiology I
• Student Laboratory Session

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Enterobacteriaceae Antigens
GNR 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 O157H7

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Escherichia coli
GNR 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)

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Escherichia coli
GNR Enterobacteriaceae

• Colony morphology

BAP beta-hemolytic
MAC dark pink diffuses around colony
EMB green metallic sheen
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Escherichia coli
GNR Enterobacteriaceae

• 1 etiologic agent of UTI
• Meningitis in 0-3 month age group

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Escherichia coli
GNR Enterobacteriaceae

• Enterohemorrhagic E. coli O157H7
• 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 O157H7 is sorbitol neg (clear on SMAC)

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Escherichia coli
GNR Enterobacteriaceae

• Gastroenteritis 4 distinct syndromes caused by
  4 distinct E. coli strains
• Usually not diagnosed by culture

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Escherichia coli - Identification
GNR Enterobacteriaceae

• Beta-hemolytic
• EMB Green metallic sheen

Citrate
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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

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Shigella sp. Identification
GNR Enterobacteriaceae
Always nonmotile!
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Shigella sp. Identification
GNR Enterobacteriaceae

• Biochemical identification should be confirmed
  with serogrouping
• Reportable disease

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Citrobacter sp.
GNR Enterobacteriaceae

• Opportunistic
• Lactose variable
• LDC LDA (-)
• C. fruendii H2S /-LDC LDA (-), H2S

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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 doesnt invade bloodstream

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Salmonella typhi
GNR Enterobacteriaceae

• Overt or primary pathogen (not NF)
• Typhoid fever
• Transmission human to human
• Specimens blood, urine then stool

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Salmonella sp. Identification
GNR Enterobacteriaceae
Glucose F H2S
LDC H2S
LIA
KIA
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Klebsiella sp.
GNR Enterobacteriaceae

• Opportunistic pathogens
• Klebsiella pneumoniae destructive pneumonia
• Muciod colony due to capsule
• Always nonmotile!

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Klebsiella sp.- Identification
GNR Enterobacteriaceae

• Muciod colony due to capsule
• Always nonmotile!

LDC
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Enterobacter sp.
GNR Enterobacteriaceae

• Opportunistic pathogen
• Muciod colony due to capsule
• ODC

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Serratia sp.
GNR Enterobacteriaceae

• Opportunistic pathogen
• Serratia marcescens
• Hospitals
• Can produce a red pigment!!
• Lactose nonfermenter
• LDC

LDC
LIA
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Proteus sp.
GNR Enterobacteriaceae

• Opportunistic pathogen
• Swarms on BAP, CHOC
• Strong urea hydrolyzer creates alkaline pH in
  urine, causes renal calculi

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Proteus sp. - Identification
GNR Enterobacteriaceae
LIA
KIA
Urea
Glucose F H2S
LDA H2S

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Providencia sp. Morganella sp.
GNR Enterobacteriaceae

• Opportunistic pathogens
• LDA

LDA
LIA
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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

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Summary - Enterobacteriaceae
GNR Enterobacteriaceae

• Identification
• Colony morphology mucoid, swarming,
  beta-hemolytic, red pigment
• Lactose fermentation
• H2S
• Nonmotile
• Deamination (LDA) positive