B-163. Detection of Escherichia coli STb Enterotoxin Variant from Diseased Pigs

C. Taillon, E. Nadeau, M. Mourez, J. D. Dubreuil;
Univ. de Montreal, Saint-Hyacinthe, QC, CANADA.

The porcine industry bears a huge loss due to morbidity and mortality resulting from enterotoxigenic Escherichia coli (ETEC) infections. STb is one of two heat-stable toxins produced by ETEC and is mostly associated with pathogenic porcine isolates. Fekete et al. (2003) (Int. J. Med. Microbiol. 292: 287-298) described a variant of STb enterotoxin detected in strain 2173. The variant comprises two changes in amino acids, His12 to Asn and Lys23 to Ile, which differed from the already reported amino acid sequence. To further investigate the frequency of this variant and to screen for other alterations at the gene level, a collection of 100 STb-positive ETEC strains isolated from 1980 to 2007 inclusively and randomly selected from diseased pigs in Quebec, Canada, was analyzed. A wide diversity of virulence genes profiles (virotypes) was detected in the 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 change from His12 to Asn in 23 of the 100 tested ETEC isolates. 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 harbouring no tested porcine fimbrial adhesin (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). The STb-variant strains were observed throughout the sampling period covered in the study. The toxicity of the reported variant needs to be evaluated in an animal model, as it could possibly account for a more potent toxic agent in pigs.