Class 1 Integron Carriage in Extended-spectrum beta-lactamase-producing K. pneumoniae

Kim, Jungmin

Abstract

Many antibiotic resistance genes found in gram-negative clinical isolates are a part of a gene cassette inserted into an integron. Incidence of the integron carriage in extended-spectrum beta-lactamases (ESBLs)-producing clinical isolates is considerably high. In this study, the presence of class 1 integron was investigated among ESBL-producing K. pneumoniae, and the genetic location of the integron and bla(ESBL) was determined to elucidate the genetic linkage of the integron and bla(ESBL) gene. Thirty-nine clinical isolates of ESBL-producing K. pneumoniae and 36 transconjugants were used. The presence of class 1 integron was examined by PCR and Southern hybridization, and the location of ESBL gene and integron was studied by Southern hybridization with the probes for bla(TEM), bla(SHV), bla(CMY-1), and integron. PCR and Southern blot hybridization studies showed that 31 of 39 (79.5%) clinical isolates and 21 of 36 (58.3%) transconjugants carried integrons. Furthermore, integron was found to be on the same conjugative plasmid on which bla(SHV-ESBL) or bla(CMY-1) gene was located, suggesting high genetic linkage of integron and blaESBL genes. A sequencing study showed that PCR-amplified inserted gene cassettes contained aminoglycoside resistance genes (aadA2, aadA5, aacA4, aadB) as well as catB5, dfrA12, dfrA17, OXA-1, and OXA-2 variant. Notably, aacA4, which had been rarely found in previous studies, was the most predominant gene cassette. In conclusion, the coincidence of an ESBL gene and class 1 integron/ gene cassette on the same conjugative plasmid has potential implications for the spread of ESBL-mediated drug resistance and may be responsible for the multi-drug resistance in these isolates.