Outbreak of multidrug-resistant Klebsiella pneumoniae carrying qnrB1 and bla(CTX-M15) in a French intensive care unit

BACKGROUND: The prevalence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae is increasing globally and is a major clinical concern. Between June 2008 and September 2009, 4% of patients in an intensive care unit (ICU) were found to be colonized or infected by strains of Klebsiella pneumoniae multiresistant to ceftazidime, ciprofloxacin, and tobramycin; an investigation was initiated and isolates were characterized by molecular typing and resistance patterns. METHODS: Antibiotic susceptibilities were determined by Vitek2(®), Etest(®), and agar dilution. Gene encoding beta-lactamases and plasmid-mediated quinolone resistance PMQR determinants (qnr, aac(6′)-Ib) were characterized by PCR, sequencing, and transfer assays. DiversiLab(®) fingerprints were used to study the relatedness of isolates. RESULTS: Fourteen isolates co-expressing bla(CTX-M15), qnrB1, and aac(6′)-Ib-cr were identified. Genotypic analysis of these isolates identified 12 clonally related strains recovered from 10 patients. The increased prevalence of bla(CTX-M15)-qnrB1-aac(6′)-Ib-cr-producing K. pneumoniae coincided with the presence in the ICU of a patient originally from Nigeria. This patient was infected by a strain not clonally related to the others but harbouring qnrB1 and aac(6′)-Ib-cr genes, a finding not hitherto observed in France. We suspected transmission of resistance plasmids followed by rapid dissemination of the multiresistant K. pneumoniae clone by cross-transmission. CONCLUSION: This study highlights the importance of microbiological screening for multidrug-resistant strains in ICUs, particularly among patients from regions in which multidrug-resistant bacteria are known to exist.