Relationship between the usage of carbapenem antibiotics and the incidence of imipenem-resistant Pseudomonas aeruginosa

Metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa isolates are resistant to almost all broadspectrum β-lactams and carbapenems. We investigated 389 P. aeruginosa isolates, collected from 29 hospitals in the Tohoku area of Japan, to determine their susceptibilities to ten antimicrobial drugs, and the rates of MBL-producing P. aeruginosa among them. Two hundred and one P. aeruginosa strains were isolated from small (group S)hospitals that had adopted imipenem as a carbapenem antibiotic, and 188 were isolated from general (group G) hospitals, which employed three or four carbapenems. MBL genes were analyzed by polymerase chain reaction (PCR) in all isolates for which the sodium mercaptoacetic acid (SMA) disk method gave positive results. The antimicrobial agents tested were imipenem, meropenem, biapenem, panipenem, piperacillin, ceftazidime, sulbactam/cefoperazone, amikacin, arbekacin, and ciprofloxacin. Sixteen (8.0%) of the 201 isolates from group S hospitals and three (1.6%) of the 188 isolates from group G hospitals were MBL-producing P. aeruginosa. In this study, the proportion of MBL-producing P. aeruginosa in group S was significantly higher than that found in group G (P < 0.01). The use of only one agent as a carbapenem antibiotic may have been one of the factors contributing to the high detection rate of MBL-producing P. aeruginosa observed in group S hospitals.