Invasion of Caco-2 Cells and Iron-acquiring Mechanisms by Enterovirulent Escherichia coli Isolates

Abstract

Escherichia coli strains were isolated as the dominating organism of faecal cultures from 65 children with acute diarrhoea, 13 with persistent diarrhoea and from 35 healthy controls in whom Salmonella sp, Shigella sp or Campylobacter jejuni were not isolated. Nor were parasites detected. Enterotoxigenic E. coli were the most commonly detected enterovirulent organism. Enteroaggregative E. coli were also isolated more frequently from cases than controls (p<0.01). The ability to invade Caco-2 cells at 28-1% was significantly more common among E. coli isolated from cases than from controls (p<0.001). None of the strains carried the enteroinvasive inv plasmid. Seven invasive strains belonged to EPEC serotypes. Of iron-acquiring mechanisms studied, transferrin-binding was expressed by 26 strains from acute diarrhoea, 4 from persistent diarrhoea and from 10 healthy children (cases-controls, p<0.001). Production of haemolysin was more common in strains isolated from cases than from controls (p<0.05) but siderophores were rarely produced (9 strains from cases and three from controls). Transferrin-binding was mediated by at least three surface proteins of M around 40 kD, 42 kD and 80 kD. In some strains the expression of these proteins was inducible, and only detected after growth in iron-depleted medium. Transferrin-binding appeared to be a common iron-acquiring mechanism expressed by enterovirulent E. coli particularly during growth in iron-depleted medium.