Susceptibility of Pseudomonas aeruginosa to antimicrobials: a 2004 French multicentre hospital study

Pseudomonas aeruginosa is a major causative agent of hospital infections. The purpose of this study was to determine the antibiotic susceptibility of P. aeruginosa in a French multicentre study and to investigate the mechanisms of β-lactam resistance. Four hundred and fifty non-repetitive strains of P. aeruginosa were collected in 15 French university hospitals in 2004. MICs of antibiotics were measured by agar dilution methods. For all the strains with MICs of ticarcillin >16 mg/L, detection and identification of the β-lactamases, quantitative determination of cephalosporinase and overproduction of the MexAB-OprM efflux pump were evaluated. The percentages of susceptible isolates were as follows: ticarcillin, 62%; ticarcillin + clavulanic acid, 61%; piperacillin, 78%; piperacillin + tazobactam, 80% (MICs ≤ 16 mg/L); aztreonam, 50%; ceftazidime, 78%; cefepime, 64%; imipenem, 83%; tobramycin, 80% (MICs ≤ 4 mg/L); amikacin, 86% (MIC ≤ 8 mg/L); ciprofloxacin, 68%; and levofloxacin, 57% (MICs ≤ 1 mg/L). Decreased susceptibility to imipenem was linked in two cases to VIM-type carbapenemase production. Overexpression of the AmpC cephalosporinase, production of acquired β-lactamases including SHV2a extended-spectrum β-lactamase and overproduction of the MexAB-OprM efflux pump were present in 16.9%, 6.5% and 22.3% of the strains, respectively. In the last decade, the overall susceptibility of P. aeruginosa hospital isolates to antibiotics has remained quite stable in France. However, the emergence of extended-spectrum β-lactamases and carbapenemases in different locations is a matter of concern.