Influence of Plasmids on the Pathogenicity and Virulence of Escherichia coli Strains of Human and Animal Origin

Abstract

Escherichia coli usually considered to be an opportunistic pathogen which constitutes a large proportion of the normal intestinal flora of men and animals. This organism can, however, contaminate, colonize and subsequently cause infection of extra intestinal sites and is a major cause of septicaemia, peritonitis, abscesses, meningitis and urogenital tract infections in men and animals. The source of these E. coli pathogens in most cases is believed to be the host’s own intestinal flora. Because of its clinical significance, E. coli has been the subject of numerous investigations in an attempt to define those virulence factors which allow it to initiate and sustain infection. E. coli is recognized as a gram-negative rod shaped bacterium, which ferments lactose and produces characteristic colonies on certain differential bacteriologic media such as MacConkey’s agar. Several schemes have been developed to characterize isolates of E. coli and to aid in the identification of pathogenic strains: serotyping, biotyping, phage-typing, colcin-typing and testing for virulence factors.