1. Gram-negative rods: Enterobacteriaceae Part II
Karen Honeycutt, M.Ed., MT(ASCP)SM
CLS 418 Clinical Microbiology I
Student Laboratory Session
Microbiology

2. Enterobacteriaceae Antigens
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

3. Escherichia coli Most common facultative organism in stool
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

4. Escherichia coli Colony morphology GNR: Enterobacteriaceae
BAP: beta-hemolytic
MAC: dark pink diffuses around colony
EMB: green metallic sheen
Microbiology

5. Escherichia coli #1 etiologic agent of UTI
GNR: Enterobacteriaceae
Escherichia coli
#1 etiologic agent of UTI
Meningitis in 0-3 month age group
Microbiology

6. Escherichia coli Enterohemorrhagic E. coli O157:H7
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

7. GNR: Enterobacteriaceae
Escherichia coli
Gastroenteritis – 4 distinct syndromes caused by 4 distinct E. coli strains
Usually not diagnosed by culture
Microbiology

8. Escherichia coli - Identification
GNR: Enterobacteriaceae
Escherichia coli - Identification
Beta-hemolytic
EMB: Green metallic sheen
MacConkey Agar
Indole
KIA
Citrate
Microbiology

9. Shigella sp. – Disease State
GNR: Enterobacteriaceae
Shigella sp. – Disease State
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

10. Shigella sp. – Identification
GNR: Enterobacteriaceae
Shigella sp. – Identification
Always nonmotile!
LIA LDC (-) & LDA (-)
MacConkey
KIA
Microbiology

11. Shigella sp. – Identification
GNR: Enterobacteriaceae
Shigella sp. – Identification
Biochemical identification should be confirmed with serogrouping
Reportable disease
Microbiology

12. Citrobacter sp. Opportunistic Lactose variable LDC & LDA (-)
GNR: Enterobacteriaceae
Citrobacter sp.
Opportunistic
Lactose variable
LDC & LDA (-)
C. fruendii: H2S +/- [LDC & LDA (-), H2S +]
LIA LDC (-) & LDA (-)
Microbiology

13. Salmonella sp. Overt or primary pathogen (not NF)
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

14. Salmonella typhi Overt or primary pathogen (not NF) Typhoid fever
GNR: Enterobacteriaceae
Salmonella typhi
Overt or primary pathogen (not NF)
Typhoid fever
Transmission: human to human
Specimens: blood, urine then stool
Microbiology

15. Salmonella sp. Identification
GNR: Enterobacteriaceae
Salmonella sp. Identification
MacConkey
Glucose “F” H2S +
LDC+ H2S +
LIA
KIA
Microbiology

16. Klebsiella sp. Opportunistic pathogens
GNR: Enterobacteriaceae
Klebsiella sp.
Opportunistic pathogens
Klebsiella pneumoniae: destructive pneumonia
Muciod colony due to capsule
Always nonmotile!
Microbiology

17. Klebsiella sp.- Identification
GNR: Enterobacteriaceae
Klebsiella sp.- Identification
Muciod colony due to capsule
Always nonmotile!
KIA
LDC+
Microbiology

18. Enterobacter sp. Opportunistic pathogen Muciod colony due to capsule
GNR: Enterobacteriaceae
Enterobacter sp.
Opportunistic pathogen
Muciod colony due to capsule
ODC+
KIA
Microbiology

19. Serratia sp. Opportunistic pathogen Serratia marcescens Hospitals
GNR: Enterobacteriaceae
Serratia sp.
Opportunistic pathogen
Serratia marcescens
Hospitals
Can produce a red pigment!!
Lactose nonfermenter
LDC +
KIA
LDC+
LIA
Microbiology

20. Proteus sp. Opportunistic pathogen Swarms on BAP, CHOC
GNR: Enterobacteriaceae
Proteus sp.
Opportunistic pathogen
Swarms on BAP, CHOC
Strong urea hydrolyzer: creates alkaline pH in urine, causes renal calculi
Microbiology

21. Proteus sp. - Identification
GNR: Enterobacteriaceae
Proteus sp. - Identification
MacConkey
LIA
KIA
Urea
Glucose “F” H2S +
LDA+ & H2S + ++
Microbiology

22. Providencia sp. & Morganella sp.
GNR: Enterobacteriaceae
Providencia sp. & Morganella sp.
Opportunistic pathogens
LDA+
KIA
MacConkey
LDA+
LIA
Microbiology

23. Summary - Enterobacteriaceae
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

24. Summary - Enterobacteriaceae
GNR: Enterobacteriaceae
Summary - Enterobacteriaceae
Identification
Colony morphology: mucoid, swarming, beta-hemolytic, red pigment
Lactose fermentation
H2S +
Nonmotile
Deamination (LDA) positive
Microbiology