Vol.53 No.8 August 2005

In vitro combined effects of antibacterial agents against clinically isolated multiple-drug resistant Pseudomonas aeruginosa (MDRP) strains

Yoko Oka

Department of Infections Disease & Infection Control, Saitama Medical School,
38 Morohongo, Moroyama-machi, Iruma-gun, Saitama, Japan

Abstract

The effectiveness of antibacterial agents against 57 strains of clinically isolated multiple-drug resistant Pseudomonas aeruginosa (MDRP) was measured by the micro-dilution method. The MIC₉₀ (the minimum inhibitory concentration of an antibiotic required to inhibit the growth of 90% of bacterial strains) values of imipenem, amikacin, and ciprofloxacin were found to be 128, 128 and 64 μg/mL, respectively. All 57 strains produced metallo-beta-lactamase, and the IMP-1 gene was detected by the polymerase chain reaction (PCR). The in vitro combined effects of the antibacterial agents were tested against 25 strains of MDRP selected by the checkerboard method after evaluation by the fractional inhibitory concentration (FIC) index. Combinations of BIPM and GM, CPFX and AZT, and CPFX and GM were found to be effective against all 25 MDRP strains. Synergy or additional effect of treatment with the combination of CPFX and AZT was observed in 64% of the strains, and there were no antagonistic effects against any MDRP strains.
We investigated DNA polymorphism in all 57 strains of MDRP by pulsed field gel electrophoresis (PFGE), and 20 of DNA polymorphisms were separated by PFGE. Ten strains of type F and 7 strains of type J were isolated from patients in the internal medicine unit of our institution, and 6 strains of type G and 7 strains of type P were isolated from patients in the surgery unit. Ten of 57 patients were diagnosed with MDRP infection and the remaining 47 were concluded to be colonized by MDRP. Eight of the 10 cases of MDRP infection were diagnosed with urinary tract infection, and the other 2 with sepsis. All 8 patients with urinary tract infection caused by MDRP survived, but both patients with MDRP sepsis died.

Key word

multiple-drug resistant Pseudomonas aeruginosa (MDRP), FIC index, IMP-1, PFGE

Received

June 24, 2005

Accepted

July 20, 2005

Jpn. J. Chemother. 53 (8): 476-482, 2005