Integron mediated antibiotic resistance genes in Shiga toxin-producing Escherichia coli and their transfer

Abstract

Approximately 7.9 and 0.6% of the Shiga toxin-producing Escherichia coli (STEC) isolates in our laboratory collection were positive for class 1 and 2 integron, respectively. These positive isolates were resistant to multiple antibiotics. However, only some of the antibiotic resistance traits were mediated by the integrons. A single gene cassette of aadA1 was identified on the class 1 integron and three gene cassettes, dfrA1, sat1, and aadA1, were found on the class 2 integron. The class 1 integron mediated antibiotic resistance genes were transferable to E. coli MG1655 during conjugation in nutrient broth. The transconjugants expressed the antibiotic resistance traits encoded by integron mediated, as well as non-integron mediated antibiotic resistance genes. Transfer of class 1 integron occurred in samples usually found in farm environments such as bovine feces and storm water. Environmental temperature and sample pH influenced the transfer frequencies of the integron mediated antibiotic resistance genes.