Colibacillosis in pigs and its diagnosis

olibacillosis is a major cause of illness and death in neonatal and recently weaned pigs. The disease is usually caused by enterotoxigenic strains of the bacterium Escherichia coli, although nonenterotoxigenic strains of that organism may also occasionally cause the disease. Diarrhea is typically fluid and profuse, and frequently results in severe dehydration and circulatory shock. Enterotoxins produced by the enterotoxigenic E. coli (ETEC) strains pathogenic to pigs include heat-labile enterotoxin (LT), and/or heat-stable enterotoxins STa (STI) or STb (STII). These organisms also produce fimbrial adhesins that mediate the adherence of the bacterium to the mucosal surface. The fimbriae produced include K88 (F4), K99 (F5), 987P (F6), F41, and F18 (F107 and 2134P). Although less common, some strains produce a Shiga toxin (Stx2e) and may cause edema disease in addition to colibacillosis. Also uncommon are strains that produce no toxins, but efface the microvilli of the epithelial cells to which they attach (Helie P, et al. Proc Int Congr Vet Soc. 1990).1 Such strains contain eae genes, which have been associated with attachment/effacement. Porcine attaching-effacing E. coli strains are very similar to those that cause diarrhea in human infants, and are known as enteropathogenic E. coli (EPEC). Because many strains of E. coli isolated from animals are nonpathogenic, it is important to identify the virulence factors produced by ETEC or EPEC strains, or the genes that encode those factors, to establish the etiology of diarrhea.