Sunday, April 5, 2009

13 - Facultative anaerobes part 3 ( ENTEROBACTERIACEAE )

• 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

No comments:

Subscribe Now: Feed

You are visitor number

Visitors currently online