Co-production of SFO-1 and DHA-1 β-lactamases and 16s rRNA methylase armA in clinical isolates of Klebsiella pneumoniae

Abstract

Objectives: To investigate the epidemiology and genetic characteristics of the plasmid-mediated extended-spectrum β-lactamase (ESBL) gene blaSFO-1 in clinical isolates of ESBL-producing Klebsiella pneumoniae and Escherichia coli. Methods: The prevalence of the blaSFO-1 gene was examined by PCR amplification. Conjugation and transformation experiments were performed and the presence of antimicrobial resistance determinants was investigated by the PCR method. The genetic environments of the blaSFO-1 and armA genes were determined by direct sequencing of plasmid pHS20. Plasmids were typed by PCR-based replicon typing. PFGE and multilocus sequence typing were performed on SFO-producing strains. Results: Of 158 ESBL-producing strains of K. pneumoniae, 3 (1.9%) carried the blaSFO-1 gene. All of the SFO-producing isolates belonged to the ST11 epidemic clone, with a single PFGE type and had high-level resistance to third-generation cephalosporins, aminoglycosides and ciprofloxacin. The blaSFO-1 gene was co-transferred with the armA, aac(6')-Ib-cr and blaTEM-1 genes by transformation, whereas the armA, blaDHA-1 and qnrB4 genes were co-transferred by conjugation. The armA genes were located within the composite transposon Tn1548 on two different plasmids in the strain 08-129. The blaSFO-1 gene was located upstream of an ampR gene from the coding region and flanked by two inverted repeats of IS26. Plasmids carrying blaDHA-1 were identified as IncFII, while the blaSFO-1-bearing plasmids were non-typeable. Conclusions: Although SFO-1 is a low-occurrence ESBL, it has been captured by a plasmid accumulating multiple resistance determinants including armA and aac(6')-Ib-cr, and accompanied by a large DHA-1-bearing IncFII plasmid in a prevalent K. pneumoniae ST11 clone. © The Author 2012. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.