Plasmids coding for enterotoxins, K88 antigen and colicins in porcine Escherichia coli strains of O-group 149.

This study was carried out to determine whether the strong epidemiological correlation observed in Sweden between production of the adhesin K88, the heat-stable (ST) and the heat-labile (LT) enterotoxins in E. coli strains of O-group 149 isolated from piglet diarrhea might be explained by linkage of their genetic determinants. From 22 different isolates plasmids coding for these virulence factors were investigated by conjugation and transduction experiments and analysis on agarose gels. The genes coding for ST production could be transferred by selection for antibiotic resistance, but behaved as transposable elements most often residing on a 55 Mdal plasmid coding for colicin B. The genes coding for raffinose fermentation and K88 antigen production were located on a 45 Mdal plasmid and the genes coding for LT production on plasmids within the 45-70 Mdal size. Thus the epidemiological importance and spread of this O-group in Sweden was explained by its stable content of two or three virulence plasmids, which could be transferred independently of one another.