Iron-suppressible production of hydroxamate by Escherichia coli isolates

Abstract

A total of 476 strains of Escherichia coli isolated from humans, pigs, cattle, poultry, potable water, or effluent were examined for iron-suppressible ability to produce hydroxamate. Isolates able to produce such material (Hyd+ isolates) are presumed to be able to carry out hydroxamate-dependent transport of iron. The percentages of Hyd+ isolates found among E. coli isolated from the feces of breast-fed babies (71%), adults (46%), milk-fed calves (32%), or poultry (28%) were significantly greater (P < 0.01) than the percentages isolated from potable water and effluent (6%) or from the feces of suckling piglets (6%), weaned pigs (6%), or weaned cattle (4%). The percentages of Hyd+ isolates found among E. coli associated with diarrhea in humans (51%), weaned pigs (7%) or calves (25%) were not significantly different (P < 0.1) from those found among strains isolated from corresponding nondiarrheic hosts. Many of the E. coli isolated from cases of E. coli bacteremia in humans and poultry were Hyd+ (64% and 83%, respectively). We conclude that ability to carry out hydroxamate-mediated transport of iron is widely distributed among natural isolates of E. coli but that the distribution of Hyd+ E. coli is not random. E. coli isolated from sources where levels of available iron might be expected to be low tend to be Hyd+. It seems that a link may exist between prevalence of Hyd+ E. coli and active host-defense based on restricted availability of iron.