Hybridization of bovine Escherichia coli isolates with gene probes for four enterotoxins (STaP, STaH, STb, LT) and one adhesion factor (K99)

Abstract

Colony hybridizations with 4 enterotoxins (STaP, STaH, STb, and LT) and 1 adherence factor (K99) gene probes were done on Escherichia coli isolated from calves. Agreement between the K99 probing and a serologic assay to detect the K99 antigen was 99% for the identification of K99+ and K99- isolates. Ninety-five of the isolates (22%) hybridized with at least 1 enterotoxin gene probe (Ent+ isolates), and 82 (19%), with the K99 gene probe. The majority of Ent+ isolates (85%) reacted with probes for STaP and K99 genes. The STaP gene was present by itself in 4 of the Ent+ isolates (4%) and with the STb gene in 6 of the Ent+ isolates (6%). Five of the Ent+ isolates (5%) carried the STb and LT genes, and none (0%) of the isolates carried the STaH gene. All but 2 of the isolates with the K99 gene also had the STaP gene. Twenty-eight isolates shown to produce STa enterotoxin in previous studies failed to hybridize with any of the enterotoxin gene probes. These 28 isolates were also phenotypically negative when the tests for enterotoxin production were repeated. These isolates probably lost their genes for enterotoxin production during storage in the laboratory.