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

Microbiology

Summary - Enterobacteriaceae

GNR: Enterobacteriaceae

• Identification– Colony morphology: mucoid, swarming,

beta-hemolytic, red pigment– Lactose fermentation

– H2S +

– Nonmotile– Deamination (LDA) positive