Increasing resistance to
quinolones,
aminoglycosides, and/or
cephamycins in extended-spectrum-β-lactamase (ESBL)-producing Enterobacteriaceae exacerbates 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-producing Klebsiella 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-producing K. pneumoniae isolates, ISCR1 was detected in 13 (72%) isolates, qnr genes (1 qnrA and 17 qnrB genes) were detected in 18 (100%), aac(6')-Ib-cr was detected in 11 (61%), and
16S rRNA methylase (all armA genes) was detected in 14 (78%). Four transconjugants were available for further analysis, and qnrB4, aac(6')-Ib-cr, armA, and bla(DHA-1) were all identified on these self-transferable bla(CTX-M)-carrying plasmids. The genetic environments of ISCR1 associated with armA, bla(DHA-1), and qnrB4 genes 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 ISCR1
element-carrying plasmids has a clinical impact and warrants close monitoring and further study.