B. NOAMANI, University of Guelph J.M. FAIRBROTHER, University of Montreal
Title
Genes and Virulence of O149:K88ac Enterotoxigenic Escherichia coli from Post-Weaning Diarrhea in Pigs
Abstract Text
The goal of this research was to determine whether strains of O149 porcine enterotoxigenic E. coli (ETEC) recovered from recent outbreaks of severe diarrhea in weaned pigs had differences in virulence genes compared with isolates of the same serogroup from diarrhea of pigs in the 1970's and 1980's (old isolates). A collection of 100 recent and 35 old isolates was investigated for the presence of known virulence genes as well as genes not previously associated with virulence. Polymerase chain reaction amplification was employed to identify the presence of 11 virulence-associated genes in all 135 O149 porcine ETEC. The estA gene for heat-stable enterotoxin a (STa) was present in 92% of the recent isolates and absent from all the old isolates. H antigen typing showed that all the old strains and 8 recent strains which lacked the estA gene had the H43 antigen, whereas the remaining recent strains, which were estA-positive, had the H10 antigen. The astA gene for enteroaggregative heat-stable enterotoxin (EAST1) was present in all 135 isolates. The eltA gene for heat-labile enterotoxin and the estB gene for heat stable enterotoxin b (STb) were detected in all but one of the isolates. There was no consistent difference in plasmid profiles of old and recent isolates but a cryptic 5.1 kb plasmid was detected in 99% of recent compared with 60% of old isolates. Suppression subtractive hybridization (SSH) was performed to identify genomic differences between a recent and an old O149:K88ac strain. Five clones identified by SSH had no homology to DNA in databases, five had high homology to LPS biosynthesis genes, and seven showed homology to F plasmid DNA. The major conclusions are that the presence of the estA gene exclusively in the O149:H10 ETEC may have enhanced the virulence of O149 porcine ETEC of this serotype; that the severe outbreaks of diarrhea in recent years were associated with the introduction of a new serotype of ETEC; and that there may be modifications to LPS in the recent isolates.
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