DIARRHOEA  Although E-coli is normally carried in the gut as a normal commensal, it may cause gastrointestinal disease ranging in severity from mild self limiting diarrhoea to hemorrhagic colitis.  Such strains fall into 5 groups associated with specific serotypes.

 The major groups of diarrhoea causing E- coli Pathogenic groupCommon serogroups Enteropathogenic E-coli(EPEC) O26,O55,O86,O111 etc Enterotoxigenic E-coli(ETEC) O6,O8,O15,O25,O27,O167 Enteroinvasive E-coli(EIEC) O28,O112,O124,O136,O143,O1 52,O154 Verocytotoxin producing E-coli (VTEC) O26,O157 Enteroaggregative E-coli (EAEC) O-untypable

ENTEROPATHOGENIC E-COLI (EPEC)  They cause infantile diarrhoea usually occuring as institutional outbreaks.  They can also cause sporadic diarrhoea in children and very rarely in adults.  Spread is through oral contamination.  In infantile enteritis there is colonisation of upper part of small intestine.  In areas of EPEC attachment brush border microvilli are lost.

 It adheres to the gut wall and causes subsequent mucosal damage.  This lesion has been termed as attachment and effacement lesion.  Such strains have been termed as AEEC (attaching and effacing E-coli).  Pathogenicity is mainly due to the production of an adhesin ‘intimin’.  EPEC also synthesize intimin receptors which is inserted into the gut wall providing binding site for intimin.

LABORATORY DIAGNOSIS OF EPEC: Sample collected-stool Plated on Mac Conkey agar Pink colonies obtained Bacteria are examined by slide agglutination with polyvalent antisera If positive then identified with monovalent antisera to individual serogroups.

ENTEROTOXINEGIC E-COLI (ETEC)  Responsible for community acquired diarrhoeal disease in areas of poor sanitation and mainly traveller’s diarrhoea.  Spread is through ware contaminated by human/animal faeces.  These strains produce heat labile (LT) or heat stable(ST) toxin or both.

 Toxin production itself is not sufficient to produce diarrhoea.the organism must bind to the intestinal epithelium.  This binding is mediated by fimbria that bind to specific receptors in the intestinal cell membrane.  These adhesins have been termed as colonisation factor antigens(CFAs).  The first CFA to be recognised was K88.loss of K88 plasmid was accompanied by loss of capacity to cause diarrhoea in piglets.

 LABORATORY DIAGNOSIS OF ETEC:  This is mainly by demonstration of toxins  LT:-  Tissue culture with mouse adrenal cells (Y1),chinese hamster cells(CHO) and vero cells.if toxin is present in culture it has a cytotonic effect on these cells i.e producing changes in cell morphology.  Others:- ELISA,RIA, Biken test (precipitin test).  ST:-  Distinguished from LT by its relative stability to heat and by rapidity of action. .

 Widely used method is infant mouse test  since it is poorly immunogenic initially immunologic tests were not performed  Now the toxin is coupled with a hapten (bovine serum albumin carrier), and the antiserum is used in RIA.  ELISA-monoclonal antibodies specific for ST are done.

ENTEROINVASIVE E-COLI (EIEC)  Causes disease resembling Shigella dysentry in individuals of all ages.  Spread mainly through ingestion of contaminated food.  A small no. of bacteria is enough to cause infection since it is resistant to acid and bile.  They enter the large intestine and multiply in the lumen.  Here they attach to the intestinal epithelial cells and are endocytosed.

 They cause lysis of the vacuole multiply within the cell and kill it.  They then spread to the neighbouring cells, cause tissue destruction.  This produces consequent inflammation which is the underlying cause of the symptoms of bacillary dysentry.  Invasiveness of the bacteria is due to an ‘outer membrane protein’ coded by a large plasmid.  The plasmid also codes for the ability for the ability to escape from the endocytic vacuole.  These strains show ‘O’ antigen cross reactivity with shigella dysentry.

LABORATORY DIAGNOSIS OF EIEC  Sereny test  Tissue culture:- whereby monolayers of Hep-2 cells and Hela cells are exposed to suspensions of the culture.after an appropriate infection period the cells are washed with gentamycin and lysozyme to wash off extra cellular organisms.the cells are then observed for intracellular organisms.

VEROCYTOTOXIGENIC E-COLI (VTEC)  They cause symptoms ranging from mild watery diarrhoea to severe diarrhoea with large amounts of blood in the stool (hemorrhagic colitis) &hemorrhagic uraemic syndrome (important complication especially in children).  Disease may occur sporadically or through outbreaks of food poisoning.  These strains produce a toxin i.e verotoxin/shiga like toxin that is cytotoxic to vero cells.

 Since it causes hemorrhagic colitis it is also known as enterohemorrhagic E-coli.  In hemorrhagic colitis initially abdominal pain is seen, followed by watery diarrhoea and finally bloody diarrhoea usually not associated with fever.  HUS is characterised by acute renal failure (major cause of renal failure in children),micro-angiopathic hemolytic anaemia and thrombocytopenia.  Vascular endothelial cells are the primary targret for the toxin.  It is usually associated with bloody diarrhoea.

 LABORATORY DIAGNOSIS OF VTEC  DNA probes for the genes encoding VT1 and VT2has been developed.  PCR with VT-specific primers has also been used to detect VTEC.  O157 VTEC strains ferment sorbitol slowly this property is used for their identification on sorbitol Mac Conkey agar. The strains are incubated over night and then tested with O157 LPS specific antiserum in a simple agglutination assay.

ENTERO-AGGRGATIVE E-COLI (EAEC)  Responsible for chronic diarrhoeal disease in certain developing countries.  They are characterised by their ability to adhere to particular laboratory-cultured cells such as Hep-2 in an aggregative or stacked brick pattern.  Most of them are O untypable but many are H typable.  The mechanism by which these strains cause diarrhoeal illness are poorly understood.

LABORATORY DIAGNOSIS OF EAEC  The only methods currently available for detecting these bacteria are the Hep-2 cell test for determining the aggregative phenotype and DNA probes.  The Hep-2 cell test involves allowing strains of E-coli to adhere to cell monolayers in vitro and observing the pattern of adhesion by microscopy.

PYOGENIC INFECTIONS  Most common cause of intra abdominal infections that result from spillage of the bowel contents.  These include: peritonitis perianal infections abscesses neonatal meningitis.

SEPTICEMIA  E-coli may invade into the blood stream and lead to fatal conditions like septic shock and systemic inflammatory response syndrome.

PREVENTION AND TREATMENT  GENERAL MEASURES: 1. Early correction of fluid and electrolye imbalance to prevent death in severe infections. 2. Avoid exposure to infecting agent. 3. Provision of safe water supplies 4. Education on hygienic practice in the handling and production of food. 5. Observing strict hygiene in hospitals to prevent spread of infantile enteritis. 6. Any infected patients should be isolated to prevent fecal spread.

 ANTIMICROBIAL PROPHYLAXIS:- 1. Some drugs reduce the incidence of diarrhoea in travellers to tropical areas:  Doxycycline  Trimethoprim  Norfloxacin and other fluoroquinolones.  However he widespread use of antibiotic prophlaxis may lead to drug toxicity and drug resistence.

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