Heterogeneity of Escherichia coli STb enterotoxin isolated from diseased pigs

To investigate the presence and frequency of estB variant(s), a collection of 100 STb-positive enterotoxigenic Escherichia coli (ETEC) strains isolated from 1980 to 2007 inclusively and randomly selected from diseased pigs in Québec, Canada, was analysed. A wide diversity of virulence gene profiles (virotypes) was detected in the strain collection. The estB gene was amplified by PCR using primers designed from the signal sequence and the C-terminal end, and the amplified fragment was sequenced using the forward primer. The translated DNA sequence revealed a His(12)-->Asn change in 23 of the 100 ETEC isolates tested. The STb-variant strains were observed throughout the sampling period covered in the study. No other STb-variant type was found in this study. All 23 variant strains were also positive for the STa enterotoxin and were resistant to tetracycline, as for strain 2173. The STb variant was associated with Stx2-positive strains (5/6) and STa : STb strains that did not harbour any of the tested porcine fimbrial adhesins (13/17). The remaining variant strains were associated with fimbriae F4 (1/40), F5 (1/6), F6 (1/1) and F18 (2/7; excluding F18 : Stx2 strains).