Dominance of international 'high-risk clones' among metallo-β-lactamase-producing Pseudomonas aeruginosa in the UK

Objectives: Carbapenem-resistant isolates of Pseudomonas aeruginosa producing metallo-β-lactamases (MBLs) are increasingly reported worldwide and often belong to particular 'high-risk clones'. This study aimed to characterize a comprehensive collection of MBL-producing P. aeruginosa isolates referred to the UK national reference laboratory from multiple UK laboratories over a 10 year period. Methods: Isolates were referred to the UK national reference laboratory between 2003 and 2012 for investigation of resistance mechanisms and/or outbreaks. MBL genes were detected by PCR. Typing was carried out by nine-locus variable-number tandem repeat (VNTR) analysis and MLST. Results: MBL-producing P. aeruginosa isolates were referred from 267 source patients and 89 UK laboratories. The most common isolation sites were urine (24%), respiratory (18%), wounds (17%) and blood (13%). VIM-type MBLs predominated (91% of all MBLs found), but a few IMP- and NDM-type enzymes were also identified. Diverse VNTR types were seen, but 86% of isolates belonged to six major complexes. MLST of representative isolates from each complex showed that they corresponded to STs 111, 233, 235, 357, 654 and 773, respectively. Isolates belonging to these complexes were received from between 9 and 25 UK referring laboratories each. Conclusions: The incidence of MBL-producing P. aeruginosa is increasing in the UK. The majority of these isolates belong to several 'high-risk clones', which have been previously reported internationally as host clones of MBLs.