Clonal analysis of Escherichia coli strains isolated from pigs with post-weaning diarrhea by pulsed-field gel electrophoresis.

The genetic diversity of 82 isolates of Escherichia coli recovered from pigs with post-weaning diarrhea was examined by restriction fragment length polymorphism (RFLP) of chromosomal DNA digested with NotI and XbaI. The isolates were of serogroups O138, O139, O141, and O149 and possessed F4 and F18 fimbrial as well as LTI, STI, STII enterotoxin and shiga toxin 2e virulence markers. The restriction pattern profiles showed a high degree of polymorphism among isolates of different serotypes and a close relationship between strains belonging to the same serological group. In addition, some bacterial strains with identical virulence determinants exhibited distinct PFGE types. The results obtained showed that RFLP analysis is a powerful tool to reveal the clonal nature and genetic differences among E. coli strains responsible for diarrhea in weaned pigs.