Genetic variability of avian Escherichia coli strains evaluated. by enterobacterial repetitive intergenic consensus and repetitive extragenic palindromic polymerase chain reaction

In this study, we tested the capability of enterobacterial repetitive inter genic consensus (ERIC) and repetitive extragenic palindromic (REP) polymera se chain reaction (PCR) to detect genetic diversity among Escherichia coli strains isolated from chickens bearing clinical signs of colibacillosis and compared the genotypes so obtained with the O:H serotypes and virulence of those strains. The DNAs from 50 avian E. coli strains and from E. coli ATC C 25922 were used to amplify ERIC and REP sequences. DNA from avian strains produced from 8 to 17 bands by ERIC-PCR and from 6 to 20 bands by REP-PCR; E. coli ATCC produced 11 bands by both methods. ERIC and REP-PCR showed go od discriminating power, and the dendograms based on the different patterns revealed extensive genetic diversity among the avian strains. Those strain s were allocated into four major clonal clusters, each one with 60% of simi larity by ERIC and REP-PCR, and those clusters corresponded to strains with different degrees of pathogenicity. However, 56% of the pathogenic strains (28/50) belonged to two out of three major clonal clusters, and 86% of the nonpathogenic strains tended to group in one cluster and one subgroup. The 32 serotypes detected were distributed in all clusters, and within a serog roup, different DNA fingerprints were observed; however, strains with same serotypes tended to form clusters with similarity coefficients greater than 80%. These results suggest that no specific serotype and genotype is respo nsible for colibacillosis and that REP and ERIC-PCR are reproducible techni ques that can improve the studies needed to clarify the pathways to the pat hogenesis of colibacillosis.