[Analyses on distribution and structure of blaCARB-2 in Klebsiella pneumoniae].

In order to characterize the structure of the beta-lactamase gene and its corresponding mobile genetic elements in Klebsiella pneumoniae, the beta-lactamase genes from 240 clinical Klebsiella pneumoniae isolates were studied. blaCARB-2, a newly characterized gene, was extensively investigated utilizing next-generation sequencing, PCR, molecular cloning, conjugation, and comparative genomics analysis. We identified 11 beta-lactamase genes among the 240 clinical Klebsiella pneumoniae isolates; the blaCARB-2 gene exists only in one specific isolate (Klebsiella pneumoniae KP1276) (1/240, 0.42%). The blaCARB-2 gene lies on a conjugative plasmid pKP1276-82, a 182,450-bp plasmid, which encodes 222 open reading frames. The plasmid has seven resistance genes, termed blaCARB-2, blaKLUC, aadA1, aadA2, cmlA1, dfrA1, and sul2. Among these genes, blaCARB-2 was identified for the first time in Klebsiella pneumoniae. Four of these resistance genes and an int gene form a class 1 integron (int-blaCARB-2-aadA2-cmlA1-aadA1). Further studies show that the blaCARB-2, aadA2, and cmlA1 genes are resistant to their corresponding antibiotics and the blaCARB-2 exhibits higher resistance activities to penicillin beta-lactams. These results reveal the possibility of horizontal transfer of the resistance genes and dissemination of resistance among bacteria of different genera or species of Enterobacteriaceae.