OXA-48-like carbapenemases in the UK: an analysis of isolates and cases from 2007 to 2014

Objectives: OXA-48-like carbapenemases have spread worldwide since 2001. We analysed patient and microbiological data for UK isolates with these enzymes as confirmed by the national reference laboratory from November 2007 - December 2014. 
Methods: MICs were determined using BSAC agar dilution. Isolates with reduced susceptibility or resistance to at least one carbapenem and high-level resistance to both piperacillin/tazobactam (MIC ≥ 64 mg/L) and temocillin (MICs ≥ 128 mg/L) were screened by PCR for blaOXA-48-like genes. The genomes of around half of the isolates were sequenced, with MLST types, resistance genes and plasmid replicon types inferred. Patient data provided by sending laboratories were reviewed. 
Results: Isolates (n=741) with OXA-48-like carbapenemases were submitted from 111 UK laboratories, representing 536 patients. Almost all (99%; 736/741) were Enterobacteriaceae, predominantly Klebsiella pneumoniae (55%; 408), and most (80%; 595) were from inpatients. WGS of 351 non-duplicate isolates identified blaOXA-48 as the most common variant, found in two-thirds (235/351) of isolates, followed by blaOXA-181 (68), blaOXA-232 (32), blaOXA-244 (10), blaOXA-484 (5) and blaOXA-245 (1). Among K. pneumoniae (163/351), E.coli (114/351), and E. cloacae (42/351), 119 STs were identified. Mapping analyses revealed that 63% (222/351) of isolates harboured plasmids that shared >99% identity to one of four known plasmids; pOXA-48a (44%; 154/351), pOXA-232 (10%; 34/351), pOXA181 (9%; 30/351), and pKP3-A (1%; 4/351); the remaining 37% of isolates harboured blaOXA-48-like in unknown environments. 
Conclusions: OXA-48-like carbapenemases are an increasing problem in the UK. This study highlights both the role of successful plasmids and polyclonal nature of their dissemination.