Characterisation of antimicrobial resistance patterns and class 1 integrons among Escherichia coli and Salmonella enterica serovar Choleraesuis strains isolated from humans and swine in Taiwan

Escherichia coli isolates from humans (n=110) and swine (n=61) and Salmonella enterica serovar Choleraesuis isolates (n=95) from swine in southern Taiwan were characterised for antimicrobial resistance patterns and class 1 integrons. All E. coli isolates and S. Choleraesuis isolates were multidrug resistant and demonstrated high resistance to beta-lactams, aminoglycosides, tetracycline, sulfonamides, spectinomycin, chloramphenicol and nalidixic acid. By polymerase chain reaction and DNA sequencing, 104 (61%) E. coli isolates and 31 (33%) S. Choleraesuis isolates were found to carry class 1 integrons. The gene cassette array dfrA12-orfF-aadA2 was the most prevalent (24%) among the human and swine E. coli isolates, whilst the gene cassette array dfrA12-orfF-aadA2-sul1 was the most prevalent (24%) among S. Choleraesuis strains. For E. coil isolates, all class 1 integrons were located on conjugated plasmids. Meanwhile, human and swine E. coli isolates carrying identical gene cassettes were genetically unrelated. Our results revealed that multidrug resistance and class 1 integrons were widely present in E. coli and S. Choleraesuis isolates obtained in Taiwan and that class 1 integrons might play an important role in contributing to the horizontal transfer of antimicrobial resistance.