Properties

Pathogenesis

Clinical findings

Laboratory diagnosis

Treatment & Prevention

Most abundant facultative anaerobe in colon & feces.

Ferments lactose.

Antigens:

O: cell wall

H: flagella

K: capsule

> 1000 antigenic types

Virulence due to:

- pili

- capsule

- endotoxin

- 2 exotoxins

Intestinal tract infection:

- adherence of organism to cells of jejunum & ileum by means of pili.

- once attached, the bacteria synthesize enterotoxins which act on the cells of the jejunum & ileum to cause diarrhea.

- acts by stimulating adenylate cyclase, increase in cAMP stimulates protein kinase, causing outpouring of fluid, potassium & chloride from enterocyte.

Systemic infection:

- capsule interferes with phagocytosis, enhancing organism’s ability to cause infections in various organs.

- sepsis: fever, hypotension, disseminated intravascular coagulation.

Diseases:

- urinary tract infection

- neonatal meningitis & septicaemia

- sepsis associated with gut; due to disease, and also post-operatively.

- diarrhoeal disease

Urinary tract infection:

- leading cause of community-acquired & nosocomial urinary tract infections.

- occur primarily in women due to short urethra & proximity to anus.

- associated with use of indwelling urinary catheters.

- involvement of bladder – cystitis: pain (dysuria) & frequency of urination.

- infection of kidney – pyelonephritis: fever, chills, & flank pain.

Neonatal meningitis:

- a major cause along with group B streptococci.

- exposure of newborn occurs during birth due to colonization of vagina in 25% of pregnant women.

Diarrhea:

- enteropathogenic: infantile gastroenteritis; bloody diarrhea, abdominal cramping & fever.

- enterotoxigenic: watery, non-bloody, self-limited, short duration diarrhea, ‘travelers’ diarrhea’.

- enteroinvasive: invade wall of colon.

- enterohaemorrhagic: verocytoxin-producing, bloody diarrhea, acute renal failure, hemolytic anemia, thrombocytopenia.

MacConkey’s agar: ferments lactose, forms pink colonies.

EMB agar: colonies have a characteristic green sheen.

Distinguishing features:

- produces indole from tryptophan.

- decarboxylates lysine.

- utilizes acetate as source of carbon.

- it is motile.

Urinary tract infection: oral sulfonamide combined with oral penicillin, e.g. ampicillin.

Sepsis:

- parenteral antibiotics.

- third generation cephalosporin, e.g., cefotaxime, with or without an aminoglycoside, such as gentamicin.

Neonatal meningitis: ampicillin & cefotaxime.

Diarrheal diseases: no antibiotics required though trimethoprim-sulfamethoxazole may shorten duration.

Prevention:

- UTI: judicious use & prompt withdrawal of catheters.

- prolonged prophylaxis with urinary antiseptics in recurrent infections.

- sepsis: prompt removal or switching site of IV lines.

- traveler’s diarrhea: prophylactic use of doxycycline, trimethoprim-sulfamethoxazole.

- caution regarding uncooked food & unpurified water.