Enterotoxigenic drug resistant plasmids in animal isolates of Escherichia coli and their zoonotic importance.

A study was undertaken to determine how widely drug resistant enterotoxigenic plasmids are distributed among the animal isolates of Escherichia coli, and their potential for exchange. Thirty-one strains of E. coli isolated from metritis, septicaemia and diarrhoea of animals were tested for the production of enterotoxins. Thirteen strains were enterotoxin producers. Five produced heat-stable enterotoxins (ST), four heat-labile (LT) and four strains produced both (LT/ST) types of enterotoxins. Most of the enterotoxin producing E. coli strains were isolated from diarrhoeal sources, followed by septicaemia and metritis. Of the 13 enterotoxigenic E. coli, nine were resistant to various antibiotics which transferred their drug resistance partially or completely into an E. coli K-12 recipient. Only one strain of serogroup 032, isolated from equine metritis, transferred ampicillin, oxytetracycline and doxycycline resistance and heat-labile enterotoxin biosynthesis determinants en bloc. Plasmid DNA analysis of the exconjugants showed the presence of a 41.8 MDa conjugative plasmid. The presence of such autotransferable enterotoxin biosynthesis replicons in their unusual ecological niches such as metritis and septicaemia suggests the ubiquitous nature of enterotoxin genes which perhaps were selected and spread due to the presence of genes for drug resistance. The potential of cross-infection of human beings from animals and vice versa via such plasmids is discussed.