Prevalence of Aminoglycoside Resistance Genes and Molecular Characterization of a Novel Gene, aac(3)-IIg , among Clinical Isolates of the Enterobacter cloacae Complex from a Chinese Teaching Hospital

Members of the complex are important opportunistic human pathogens capable of causing a wide variety of infections. During recent decades, aminoglycoside-resistant complex isolates have increasingly been reported and have become a major concern. Here, we employed high-throughput sequencing in combination with specific PCR assays to investigate the prevalence of aminoglycoside resistance genes among 170 isolates of the complex collected from a teaching hospital in Wenzhou, China. A total of 12 known genes [ , , , , , , , , , , , and ] and 1 novel gene [ ] were identified, with (71.18%), (55.29%), and (52.35%) being the most prevalent, and was detected with a positive rate of 21.76% (37/170). The gene was 810 bp in length and encoded a protein that shared 72 to 78% identities with previously known AAC(3)-II aminoglycoside 3- -acetyltransferases. The MICs of gentamicin and tobramycin were 512 μg/ml and 64 μg/ml, respectively, when was cloned into DH5α. All -positive isolates exerted broad aminoglycoside resistance profiles, mediated by the coexistence of multiple resistance genes. Moreover, aminoglycoside resistance and resistance genes were found to be transferable in most strains (24/37). Nevertheless, pulsed-field gel electrophoresis (PFGE) and dendrogram analysis showed clonal diversity among these isolates. S1 nuclease PFGE, Southern hybridization, and whole-genome sequencing indicated that was located on transferable as well as nontransferable plasmids of various sizes. The analysis of the genetic environment suggested that is embedded within a class 1 integron, with IS playing an important role in its mobility.