Download E.coli - Yengage

Enterobacteriaceae
General Features of Enterobacteria
Present in large intestine
Gram negative bacilli
Aerobic or facultative anaerobic
Motile by peritrichate flagella or non motile
Grow on ordinary media (non fastidious)
Catalase + ve & oxidase -ve
Classification of Enterobacteriaceae
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Based on lactose fermentation – oldest method :
Lactose fermenters e.g. Escherichia, Klebsiella.
Late lactose fermenters e.g. Shigella sonnei
Non lactose fermenters e.g Salmonella, Shigella
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Commensal intestinal bacteria: LF
Intestinal pathogens: NLF
Escherichia coli
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Named after Escherich, first to describe
colon bacillus
Normal flora of the human & animal
intestine.
Detection of E.coli in the drinking water –
indicates recent pollution with human or
animal feces.
Virulence Factors
Two types of virulence factors: Surface Ags & Toxins
1. Surface Antigens
– LPS surface O Ag – endotoxic activity, protects from
phagocytosis and bactericidal effects of complement
– Envelope or K Ag – protects against phagocytosis and
antibacterial factors inserum
– Fimbriae – colonisation factors, found in strains causing
diarrhoea and urinary tract infections
2. Toxins (Exotoxins) –
– Enterotoxins – pathogenesis of diarrhoea
- 3 types : LT (heat labile toxin),
ST (heat stable toxin) &
VT (verocytotoxin or shiga- like toxin)
Pathogenicities/ Clinical Infections
1. Urinary tract infection
2. Diarrhoea
3. Pyogenic infections
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Wound infection, especially after surgery of lower
intestinal tract.
Peritonitis.
Biliary tract infection.
Neonatal meningitis.
4. Septicemia – can lead to fatal conditions like
- Septic shock
Lab Diagnosis of UTI
Specimens:
Microscopy
Wet mount
Gram stain
Urine Culture
Urine Mid stream urine
(MSU)
Pus cells / hpf
Bacteria / crystals/
casts
Gram negative bacteria
Kass semi-qauntative method
Standard loop technique
To know significant bacteriuria
Lab Diagnosis of E. coli UTI
Significant
bacteriuria
> 105 organism / ml of MSU
Culture
BA / MAC : LF (flat)
Identification tests
I M Vi C test: + + - -
Diarrheagenic E.coli
• Enteropathogenic E.coli (EPEC)
• Enterotoxigenic E.coli (ETEC)
• Enteroinvasive E.coli (EIEC)
• Enterohemorrhagic E.coli (EHEC) or
Verotoxigenic E.coli (VTEC)
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