Emergence of extended-spectrum beta-lactamases in Pseudomonas aeruginosa: about 24 cases at Rouen University Hospital

AIM OF THE STUDY: This retrospective study was conducted in order to characterize mechanisms of resistance to beta-lactams and clonality of 24 isolates of Pseudomonas aeruginosa. These strains were isolated from patients hospitalized in Rouen University Hospital between August 2004 and December 2006 and were resistant to cefepime and/or ceftazidime (PMR) by a mechanism not only related to overproduction of the cephalosporinase. PATIENTS AND METHODS: Clinical strains of PMR were characterized by conventional biochemical methods, antibiotic susceptibility testing by disk diffusion in agar with or without cloxacillin and RAPD for genetic comparison. Identification of beta-lactamase was performed by PCR amplification followed by sequencing of bla genes. RESULTS: All strains produced the extended-spectrum beta-lactamase (ESBL) TEM-116. Epidemiological study identified eight unrelated strains, eight related strains originating from a single unit, three related strains isolated in different wards and five related strains coproducing TEM-116 and SHV-2a but isolated in different units. Detection of ESBL in these strains was difficult due to a low level of ESBL production. CONCLUSION: This is the first report of TEM-116 in France in 24 strains of P. aeruginosa and its association with SHV-2a in five cases. SHV-2a has been described in P. aeruginosa in France but not TEM-116 which was recently reported in this species, in China and in Netherlands (in a strain coproducing SHV-12). ESBL detection in PMR remains indispensable since these strains can cause therapeutic failures.