• Escherichia :
o Most common inhabitants of intestinal tracts.
o Food & water presence indicates fecal contamination; indicator bacterium
o Endogenous spread (septacemia, urinary tract infections, meningitis) or food-water borne transmission (gastroenteritis, travellers diarrhea)
o Antigenic composition complex: 170, 57 H and several K antigens (epidemiological & specific serotypes associated with increased virulence (H157:O7)
o Septicimia: Focus of infection is urinary tract or intestine and spreads to bloodstream (higher incidence of death in immunocmpromised patients)
o Urinary tract infection: 80% = community aquired or hospital aquired. 10 specific serotypes usually involved (eg 01, 02, 016, 075) & origin is from gastrointestinal tract.
o Pathogenecity --serotypes more adhesive to uroepithelial cells than other serotypes
o Meningitis: E.coli & B streptococci cause 75%. Serotype K1
o Gastroenteritis: 4 groups; enterotoxigenic (ETEC) causes travellers & infant diarrhea, pathogenecity similar to V. cholera toxin ie stimulates hypersecretion of fluids & electrolytes in gastrointestinal tract , not serotype specific, produce heat labile & heat stable plasmid mediated enterotoxins, not serotype specific (NA probing, tissue culture or animal models & not serotyping for identification. Enteroinvasiveness (EIEC)
• Klebsiella :
o Capsulated
o K. pneumoniae-- pneumonia (old or immunocompromised eg alcoholics); also causes septecimia in hospital pediatric wards
• Serratia :
o S. marcesens- red pigmented colonies
o Causes hospital aquired infections (nosocomial) like Enerobacter
o Urinary & respiratory tract infection
o Isolated from sterile saline solution, catheters
• Proteus :
o Extremely motile
o P. mirabilis-- urinary tract infection; produces urease & splits urea to CO2 and NH3 to increase pH & therefore facilitate renal stone formation & uroepithelium toxicity.
o Pili decreases phagocytosis & therefore decreases virulence unlike E. coli .
• Erwinia :
o Plant pathogens (phytopathogens)
o Produce pectinase which hydrolyse pectin between plant cells & cause plants to rot
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