Shiga-like toxin production and attaching effacing activity of Escherichia coli associated with calf diarrhea

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Abstract
SUMMARY: Four hundred twenty-nine isolates of Escherichia coli from calves were tested for the production of HeLa cell cytotoxin(s). Isolates that produced enough cytotoxin to be detected in culture supernatants of iron-depleted broth were considered to produce increased amounts of cytotoxins. Isolates also were tested for homology with a DNA probe for a gene that encodes localized adherence of human enteropathogenic E coli. Four isolates produced increased amounts of cytotoxin that was neutralized by Shiga antitoxin (toxin designated as Shiga-like toxin-I [slt-I]). A 5th isolate produced increased amounts of cytotoxin (slt+) that was not neutralized by the Shiga antitoxin, but was neutralized by antitoxin against a variant of slt (toxin designated as slt-II). None of the isolates hybridized with the probe for the localized adherence gene. Three of the slt+ isolates belonged to human enteropathogenic E coli serogroups O26 and O111. All 5 of the slt+ isolates were from calves with diarrhea, but none of the 5 slt+ isolates contained genes for classic heat-labile or heat-stable enterotoxins, for K99 fimbriae, or for invasiveness; neither did any of them adhere to HeLa cells in culture. Three of the 5 slt+ isolates had attaching and effacing activities when inoculated into ligated intestinal loops of rabbits. One of the isolates with attaching and effacing activity in rabbits was originally isolated from a calf with lesions characteristic of those produced by attaching effacing E coli (aeec). Calves inoculated with this slt+ aeec isolate developed focal colonic lesions characteristic of those produced by aeec, but did not develop diarrhea. Seemingly, increased slt production and aeec activity occur together in some E coli isolates from calves in the United States. However, the prevalence of such isolates in the collection studied was low.