Detection of Pseudomonas aeruginosa isolates producing VEB-type extended-spectrum β-lactamases in the United Kingdom

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Abstract

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.

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