Comparison of necrotoxigenic Escherichia coli isolates from farm animals and from humans

Necrotoxigenic Escherichia coli (NTEC) isolated from animals and humans can belong to the same serogroups/types and produce or carry the genes coding for fimbrial and afimbrial adhesins of the same family, P, S, F17, and/or A FA, raising the question of a potential zoonotic source of human infection. The main purpose of this study was to compare 239 NTEC1 strains (45 from c attle, 65 from humans and 129 from piglets) and 98 NTEC2 strains from cattl e, using a uniform and standardized typing scheme. The O serogroups and the biotypes recognized amongst NTEC1 and NTEC2 strains were quite varied, alt hough some were more frequently observed (serogroups O2, O4, O6, O8, O18, O 78, and O83 and biotypes 1, 2, 5, 6, and 9). Hybridization, results with ge ne probes for the P family (PAP probe), S family (SFA probe), AFA family (A FA probe), F17 family (F17 probe) of fimbrial and afimbrial adhesins, could differentiate most NTEC1 strains, which are PAP-, SFA- and/or AFA-positive , from NTEC2 strains, which are mainly F17- and/or AFA-positive, but were o f no help in differentiating between NTEC1 strains from cattle, humans, and piglets. All but seven (98%) NTEC1 and NTEC2 strains were serum resistant, 199 (59%) produced an aerobactin, and colicin (I, V, or unidentified) was produced by 22-34% of them. On the other hand, more than 90% of the NTEC1 s trains were haemolytic on sheep blood agar compared with only 40% of the NT EC2 strains. Production of a classical haemolysin, active on sheep erythroc ytes, and hybridization with the PAP probe were associated in a majority of NTEC1 strains (63-81%), but very rarely in NTEC2 strains (3%). Production of enterohaemolysin and hybridization with the PAP probe were much less fre quently associated in NTEC strains (1-9%). It was thus possible neither to completely differentiate NTEC1 strains from cattle, humans, and pigs, nor t o define a signature for the NTEC strains. Necrotoxigenic E. coli must stil l be identified on the basis of the production of the Cytotoxic Necrotizing Factors I or 2 (or of their encoding genes) and complete differentiation o f NTEC1 strains from cattle, humans, and piglets, use additionnal methods. (C) 1999 Elsevier Science B.V. All rights reserved.