CTX-M-15 in combination with aac(6')-Ib-cr is the most prevalent mechanism of resistance both in Escherichia coli and Klebsiella pneumoniae, including K. pneumoniae ST258, in an ICU in Uruguay.

The objectives of this study were (i) to determine the extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae (ESBL-EcKp) clones circulating in an intensive care unit (ICU) in Uruguay between August 2010 and July 2011, (ii) to characterise the ESBL and plasmid-mediated quinolone resistance (PMQR) genes of the studied isolates and (iii) to determine the virulotype of the clinical isolates. Clinical and gut-colonising ESBL-EcKp from ICU patients were studied. Bacterial identification and antibiotic susceptibility determination were performed using a VITEK(®)2 system. Detection of ESBL, KPC and PMQR genes was performed by PCR and sequencing. Clonality was assessed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). In total, 54 ESBL-EcKp isolates (40 K. pneumoniae and 14 E. coli), with or without PMQR genes, were recovered from 30 of 68 inpatients. Forty-seven isolates were CTX-M-15-producers (36 as a single ESBL and 11 together with CTX-M-14). In addition, four isolates produced CTX-M-14, two produced CTX-M-2 and one produced SHV-5. No carbapenemases were detected either in E. coli or K. pneumoniae isolates. Among the ESBL-producing isolates, 42 also harboured PMQR genes: 27 aac(6')-Ib-cr; 14 aac(6')-Ib-cr and qnrB; and a single isolate carrying only qnrB. K. pneumoniae ST258, ST48 and ST16 and E. coli ST10 and ST405 were detected in 46/54 isolates, including 9 clinical isolates. In conclusion, non-KPC-producing K. pneumoniae ST258 harbouring different ESBL and PMQR genes was the main clone disseminated in the ICU. Extensive surveillance measures must be implemented to prevent the emergence of acquired plasmid-encoded blaKPC by ST258 K. pneumoniae.