Spread of ISCR1Elements ContainingblaDHA-1and Multiple Antimicrobial Resistance Genes Leading to Increase of Flomoxef Resistance in Extended-Spectrum-β-Lactamase-Producing Klebsiella pneumoniae

Abstract

ABSTRACTIncreasing resistance to quinolones, aminoglycosides, and/or cephamycins in extended-spectrum-β-lactamase (ESBL)-producingEnterobacteriaceaeexacerbates the already limited antibiotic treatment options for infections due to these microbes. In this study, the presence of resistance determinants for these antimicrobial agents was examined by PCR among ESBL-producingKlebsiella pneumoniae(ESBL-KP) isolates that caused bacteremia. Pulsed-field gel electrophoresis was used to differentiate the clonal relationship among the isolates studied. Transferability and the location of the resistance genes were analyzed by conjugation experiments, followed by DNA-DNA hybridization. Among the 94 ESBL-KP isolates studied, 20 isolates of flomoxef-resistant ESBL-KP were identified. They all carried a DHA-1 gene and were genetically diverse. CTX-M genes were found in 18 of the isolates. Among these DHA-1/CTX-M-producingK. pneumoniaeisolates, ISCR1was detected in 13 (72%) isolates,qnrgenes (1qnrAand 17qnrBgenes) were detected in 18 (100%),aac(6′)-Ib-crwas detected in 11 (61%), and 16S rRNA methylase (allarmAgenes) was detected in 14 (78%). Four transconjugants were available for further analysis, andqnrB4,aac(6′)-Ib-cr,armA, andblaDHA-1were all identified on these self-transferableblaCTX-M-carrying plasmids. The genetic environments of ISCR1associated witharmA,blaDHA-1, andqnrB4genes in the four transconjugants were identical. Replicon-type analysis revealed a FIIA plasmid among the four self-transferable plasmids, although the other three were nontypeable. The cotransfer of multiple resistance genes with the ISCR1element-carrying plasmids has a clinical impact and warrants close monitoring and further study.