Molecular analysis of NDM-1-producing enterobacterial isolates from Geneva, Switzerland

Objectives: To analyse the mechanisms responsible for decreased susceptibility or resistance to carbapenems in several enterobacterial isolates recovered in 2009-10 in Geneva University Hospitals, Switzerland. Methods: PCR and sequencing were used to identify beta-lactamases, 16S RNA methylases and plasmid-mediated quinolone resistance genes. The transferable properties of the plasmids were analysed, as well as their plasmid type. The strains were typed by multilocus sequence typing. Results: Three patients were found to be positive for NDM-1-producing enterobacterial isolates (one with Escherichia coli and Klebsiella pneumoniae, one with K. pneumoniae only and one with Proteus mirabilis), where NDM-1 stands for New Delhi metallo-beta-lactamase-1. The bla(NDM) (1) carbapenemase gene was detected in all isolates in addition to genes encoding narrow-spectrum beta-lactamases (TEM-1, SHV-11, OXA-1, OXA-9 and OXA-10), extended-spectrum beta-lactamases (CTX-M-15, CMY-16 and CMY-30), ArmA and quinolone resistance determinants (Qnr). The bla(NDM-1) gene was located on conjugative IncA/C- or IncF-type plasmids. Upstream of the bla(NDM-1) gene, part of ISAba125, previously identified in NDM-1-negative Acinetobacter baumannii, was found. Downstream of the bla(NDM-1) gene, variable sequences were found. Conclusions: This work constitutes the first identification of NDM-1 producers in Switzerland. Interestingly, patients from whom these NDM-1-producing isolates were recovered had a link with the Indian subcontinent or the Balkans.