Characterization of multidrug-resistance phenotypes and genotypes of Escherichia coli strains isolated from swine from an abattoir in Osaka, Japan

A total of 455 highly tetracycline-resistant Escherichia coli strains were isolated from 84 healthy swine from abattoirs and it was found that 56.9, 43.1, 22.2, 15.4, 2.6 and 1.5% of strains were resistant to chloramphenicol, ampicillin, kanamycin, trimethoprim-sulphamethoxazole, ofloxacin and gentamicin respectively. Interestingly, E. coli strains isolated from certain finisher hog groups exhibited resistance against 2-7 antimicrobials, but strains isolated from multiparous sow groups in each herd were resistant to only 2-4 antimicrobial agents. When randomly selected 108 tetracycline-resistant isolates were tested for the presence of resistance genes, the following genes tet(A) (n=6), tet(B) (n=95), tet(D) (n=1) or both tet(A) and tet(B) (n=6) were found to be distributed among them. Furthermore, 52 isolates carried the integrase 1 gene and 24 strains gave five different PCR amplicon profiles using primers from the variable region of integron. Extensive nucleotide sequence analyses of these amplicons revealed the presence of dhfrI, dhfrXII, dfr17, aadA, aadA2, aadA5, aadA21, aacA4 and catB3 genes which code for different antibacterial resistance proteins.