Genotypic Colonization Factors Prevalence of Enterotoxigenic E. coli Among a Rural Paediatric Population Using Multiplex PCR

Abstract

A. Morphology, physiology and taxonomy of E. coli

Enterobacteriaceae consists of both commensal and pathogenic enteric bacteria that live in the intestinal tract of man and animals(I,Sl. Within the family Enterobactriaceae, the genus Escherichia< 1 2 3 4) contains mostly motile gram­ negative bacilli. A species belonging to that genus is Escherichia coli (E. coli). E. coli is the predominant, non-pathogenic facultative anaerobe of the human colonic flora<6'7l.

The gastrointestinal tract of most warm-blooded animals is colonized by E. coli within hours or a few days after birth. The human bowel is usually colonized within 40 hours of birth. E. coli can adhere to the mucus overlying the large intestine. Once established, an E. coli strain may persist for months or years. Resident strains shift over a long period (weeks to months), and more rapidly after enteric infection or antimicrobial chemotherapy that perturbs the normal flora. The basis for these shifts and the ecology of Escherichia coli in the intestine of humans are poorly understood despite the vast amount of information on almost every other aspect of the organism's existence. The entire deoxyribonucleic acid (DNA) sequence of the E. coli genome has been known since 1997(6 .

E. coli is easily recovered from fecal specimens on standard laboratory agar at

37"C under aerobic conditions<2l. E. coli in stool are most often recovered on MacConkey or Eosin Methylene-Blue (EMB) agar, which selectively grow members of Enterobacteriaceae and permit differentiation of enteric organisms on the basis of morphology0 l. Colonies of most E. coli species appear as large, pink colonies on MacConkey agar as a result of lactose fermentation. They are uniformly circular with