1. ESCHERICHIA Diseases: @ Urinary tract infections. @ Neonatal meningitis @ Traveller's watery diarrhoea @ Some strains are enterohemorrahagic and cause bloody diarrhoea.

3. Antigens: # the O or cell wall antigen # the H or flagellar antigen # the K or capsular antigen.. @ There are more than 150 (O), 50 (H), and 90 (K) antigens @ Various combinations of these result in about 1000 antigenic types of E coli. @ Specific serotypes are associated with certain diseases: O55 and O 111 cause outbreaks of neonatal diarrhoea.

5. @ Antisera typing is used in epidemiology @ E.coli is the most abundant after Bacteroides in the colon. Pathogenesis: @ Has several components to cause intestinal tract infection and systemic infections, e.g: # Pili # Capsule # Endotoxin # two exotoxins (enterotoxins).

7. Mechanism of Intestinal Tract Infection: @ First step is adherence of E.coli to cells of jejunum & ileum by means of pili that protrude from E.coli surface. @ Once attached, E.coli synthesizes either or both of the following 2 enterotoxins: (1) High molecular wt. heat-labile toxin (LT) (2) Low molecular wt. heat-stable toxin (ST)

9. @ The toxins catalyze the secretion of ADP-ribose. ADP-ribose stimulates production of Gs protein. @ Gs protein stimulates production of adenylate cyclase enzyme @ Adenylate cyclase enzyme stimulates overproduction of cyclic AMP. @ Cyclic AMP stimulates production of Na,Cl,K, bicarbonate, watery diarrhea

11. @ Some E.coli strains are enteroinvasive and cause disease by invasion of the large intestine epithelium causing bloody diarrhoea and presence of inflammatory neutrophil cells in stool. @ Other strains are entero-hemorrahagic (those with the O157:H7 serotype), and cause bloody diarrhoea without inflammatory neutrophils in the stool

13. @ These O157:H7 strains produce verotoxin (toxic to vero monkey) which is toxic to the cells lining the colon. @ O157:H7 strains are associated with outbreaks of diarrhoea following ingestion of undercooked hamburger at fast-food restaurants. @ Bloody diarrhoea caused by O157:H7 can complicate into the hemolytic-uremic syndrome, that leads to hemolytic anemia thrombocytopenia, & renal failure

15. Systemic Infections: @ The capsule and the endotoxin play a role in systemic diseases. @ Capsule interferes with phagocytosis so helps E.coli to cause infections. @ E coli strains that cause neonatal meningitis have a specific capsular type called the K1 antigen. @ The E.coli endotoxin of the cell wall causes fever, hypotension, and disseminated intravascular coagulation.

17. @ Certain O serotypes of E coli cause urinary tract infections. @ These strains have pili that help them to adhere to specific receptors on the urinary tract epithelium. @ The binding site on these receptors are dimers of galactose (Gal-Gal dimmers).

19. Clinical Findings: (1) Community-acquired UTIs: @ Occur mainly in women; Due to: # A short urethra # Proximity of urethra to the anus # Colonization of vagina by faecal flora. (2) Nosocomial UTIs: @ Associated with indwelling urinary catheters; leads to: # Cystitis (dysuria, frequency of urination). # Pyelonephritis (fever, chills, flank pain).

21. (3) Neonatal meningitis: @ Newborn is infected during birth due to colonization of vagina by E.coli. (4) Hospital-acquired sepsis: @ It arises from urinary, biliary, or peritoneal infections. (5) Watery, non-bloody diarrhoea: @ Self-limited, 1-3 days duration, associated with traveller's diarrhoea.

23. (6) Bloody diarrhoea: @ Dysentery-like syndrome, caused by enteropathogenic E coli (abdominal cramps, fever). @ O157:H7 strains of E coli cause bloody diarrhoea complicated by haemolytic ureamic syndrome.

25. Laboratory Diagnosis: Specimens: @ stool, urine, blood, swabs, CSF, etc. Culture: @ On blood, EMB, Mac Conkey agar. @ E coli fermenting lactose (pink colonies), E coli not fermenting lactose (colorless). @ EMB agar shows green sheen colonies.

27. Identification: @ Distinguished from other lactose- fermenting gram-negative rods by: # Produces indole from tryptophan. # It decarboxylates lysine # it utilizes acetate as a source of carbon # it is motile. # E coli O157:H7- sorbitol negative (pale) (distinction from other strains of E coli) @ Isolation of ETEC & EPEC in diarrhoeal cases is not done routinely.

29. Prevention @ Only general measures: # Careful use & prompt catheters removal # Prolonged use of urinary antiseptic drugs (nitrofurantoin). # Prompt removal of or switching the site of intravenous lines. # For traveller's diarrhoea give doxycycline ciprofloxacin, co-trimoxazole or Pepto- Bismol. # Avoid uncooked foods and impure water

31. Treatment @ Depends on the site of infection: # Uncomplicated lower UTI: Treated for 1-3 days by oral co-trimoxazole or ampicillin. # E coli sepsis: Treated by parenteral cefotaxime, with or without gentamicin. # Neonatal meningitis: Treated by giving ampicillin and cefotaxime together. # Diarrheal diseases: Treated by oral co- trimoxazole or loperamide (Imodium)