JAC Advance Access published online on September 26, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn400
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Original research |
Detection of Pseudomonas aeruginosa isolates producing VEB-type extended-spectrum β-lactamases in the United Kingdom
1 Centre for Infections, Health Protection Agency, 61 Colindale Avenue, London NW9 5EQ, UK 2 Department of Microbiology, Wrightington, Wigan and Leigh NHS Trust, Wigan, UK 3 Whiston Hospital, St Helens and Knowsley Teaching Hospitals NHS Trust, Prescot, Merseyside, UK 4 Department of Microbiology, The Great Western Hospital, Swindon, UK 5 Department of Medical Microbiology, Salisbury NHS Foundation Trust, Salisbury, UK
Received 10 July 2008; returned 22 August 2008; revised 27 August 2008; accepted 29 August 2008
* Corresponding author. Tel: +44-20-8327-7255; Fax: +44-20-8327-6264; E-mail: neil.woodford{at}hpa.org.uk
Objectives: The aim of this study was to investigate the presence of VEB enzymes among Pseudomonas spp. referred to the UK's national reference laboratory and with phenotypic evidence of extended-spectrum β-lactamase (ESBL) production.
Methods: Antibiograms were analysed for Pseudomonas spp. referred from November 2003 to November 2007. Isolates with 
4-fold ceftazidime/clavulanate synergy were screened for blaVEB alleles. Genes encoding metallo-β-lactamases (blaMBL) were sought in isolates with positive imipenem/EDTA synergy tests. Selected PCR products were sequenced. PFGE of SpeI-digested genomic DNA was used to compare isolates.
Results: Forty-nine (3.7%) of 1338 Pseudomonas spp. were considered potential ESBL producers; 40 were recovered for molecular testing. blaVEB alleles were detected in 32 Pseudomonas aeruginosa isolates, comprising diverse PFGE types, from 12 UK hospitals and 1 in India. One UK centre referred 15 isolates with VEB-1 enzyme; these were serotype O15, representing a single PFGE-defined strain that also produced VIM-10 metallo-carbapenemase. This strain was resistant to all β-lactams, aminoglycosides and ciprofloxacin, remaining susceptible only to colistin (MICs 
1 mg/L). Two other P. aeruginosa isolates co-producing both VEB and VIM enzymes were received from two other UK hospitals; one isolate represented inter-hospital spread of the O15 strain and the second was distinct.
Conclusions: VEB enzymes have not been reported previously in the UK, but were produced by 80% of Pseudomonas spp. with phenotypic evidence of ESBL production. They co-existed with VIM carbapenemases in two strains, with one responsible for a major hospital outbreak. The incidence of ESBLs may be underestimated in Pseudomonas because ESBL phenotypes can be masked by other β-lactam resistance mechanisms.
Key Words: ESBL , VIM metallo-carbapenemase , international clone , hospital outbreak
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