A Pseudomonas aeruginosa isolate producing the GES-5 extended-spectrum beta-lactamase.

Sir, Pseudomonas aeruginosa is a common nosocomial pathogen, and has an inducible, naturally occurring cephalosporinase that confers resistance to aminopenicillins and narrow-spectrum cephalosporins such as cefalotin and cefoxitin. Resistance to extended-spectrum cephalosporins may arise from the overexpression of this cephalosporinase, acquired b-lactamases or both. The so-called clavulanic acid-inhibited extended-spectrum b-lactamases (ESBLs) have been frequently reported in members of the family Enterobacteriaceae since the early 1980s, and have been described in P. aeruginosa only more recently. To date, five types of class A (TEM, SHV, PER, VEB and IBC/GES) and class D (OXA) ESBLs have been detected in P. aeruginosa. There are currently nine known GES-type ESBLs. So far, four of these GES types (GES-1, -2, -8 and -9) have been found in P. aeruginosa. 6 We report in this article the discovery of GES-5 in a ceftazidime-resistant P. aeruginosa isolate in China. P. aeruginosa PK1278 was isolated in July 2004 at the PLA 304th Hospital in Beijing, China, from the blood of a 35-year-old patient who suffered from a burn on his right leg and developed a wound infection. He was first treated with cefotaxime and amikacin. These antibiotics were discontinued and he was given imipenem. He improved and was discharged 30 days later. He had not received antibiotic therapy prior to the admission or travelled outside China. The isolate was identified by Vitek Gram-negative identification cards (bioMérieux-Vitek, Inc., Hazelwood, MO, USA). The antimicrobial susceptibility profile of P. aeruginosa PK1278 was determined using the disc diffusion and agar dilution methods according to the NCCLS. Whole cell DNA from P. aeruginosa PK1278, prepared by a rapid alkaline lysis procedure, was used as a template in PCR assays. PCR was performed using the primers for blaTEM, blaSHV, blaGES, blaPER, blaVEB and blaOXA listed in Table 1, which were designed based on all six genotypes of ESBL genes published in GenBank. PCR conditions were: 3 min at 93 C; 40 cycles of 1 min at 93 C, 1 min at 55 C and 1 min at 72 C; and, finally, 7 min at 72 C. The amplicons were purified with PCR Clean Up Kits (Roche Molecular Biochemicals, Mannheim, Germany) and were sequenced on an ABI PRISM377 sequencer analyser (Applied Biosystems, Foster City, CA, USA). According to antibiotic susceptibility testing by disc diffusion, P. aeruginosa PK1278 was only susceptible to imipenem and meropenem and resistant to ceftazidime, ceftriaxone, cefepime, cefoperazone/sulbactam, piperacillin/tazobactam, ciprofloxacin and amikacin. The isolate showed resistance to ceftazidime (MIC > 256 mg/L), ceftriaxone (MIC > 256 mg/L), cefepime (MIC 64 mg/L), cefoperazone/sulbactam (MIC 64 mg/L), piperacillin/tazobactam (MIC 128 mg/L), ciprofloxacin (MIC 2 mg/L) and amikacin (MIC 256 mg/L), and intermediate resistance to imipenem (MIC 8 mg/L) and meropenem (MIC 8 mg/L). P. aeruginosa PK1278 was only positive for blaGES in PCR assays. The nucleotide sequence derived from the blaGES amplicon (GenBank accession number AY953375) was submitted to BLAST 2.0 and found to be identical with blaGES5 which contained three silent mutations at nucleotide positions 117 (C! A), 435 (G! C) and 513 (G! T) compared with blaGES-5 from Escherichia coli (GenBank accession number AY494717). This is the first report of GES-5 in P. aeruginosa worldwide.