Vol.60 No.4 July 2012
Combined effects of triple antibacterial agents in vitroagainst multidrug-resistant Pseudomonas aeruginosa
1)Department of Clinical Support, Hiroshima University Hospital
2)Department of Clinical Pharmacotherapy, Institute of Biomedical and Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, Japan
3)Department of Clinical Laboratory, Hiroshima University Hospital
4)Department of Infectious Diseases, Hiroshima University Hospital
Abstract
This in vitro study examined the combined effects of triple antibacterial agents against multidrug-resistant Pseudomonas aeruginosa(MDRP). The tested isolates in Hiroshima University Hospital were 40 strains which met the reporting criteria for MDRP, that is, the minimum inhibitory concentration(MIC) was ≥16 μg/mL of meropenem(MEPM), ≥4 μg/mL of ciprofloxacin(CPFX) and, ≥32 μg/mL of amikacin(AMK). Combinations of antibacterial agents were: i) MEPM, CPFX and AMK, and ii) piperacillin(PIPC), aztreonam(AZT) and arbekacin(ABK). Using the original checkerboard plates, MIC values were determined for single, double and triple combinations. Based on the MIC values, fractional inhibitory concentration index values were calculated and the combined effects (synergetic action or additional action) were evaluated. In terms of the combination i), MEPM+CPFX+AMK showed the greatest combined effects against 24 strains (60.0% of 40 strains), decreasing in the mean MIC value of each antibacterial agent. The proportion of strains which met the reporting criteria for MDRP (the MIC was ≥16 μg/mL of MEPM, ≥4 μg/mL of CPFX, and ≥32 μg/mL of AMK) decreased from 100% (40/40) to 42.5% (17/40). In terms of the combination ii), PIPC+AZT+ABK showed the greatest combined effects against 31 strains (77.5% of 40 strains), decreasing in the mean MIC value of each antibacterial agent. These combined effects of triple antibacterial agents against MDRP tested in vitro should be verified and compared with those of other combinations.
Key word
multidrug-resistant Pseudomonas aeruginosa, checkerboard, FIC index
Received
February 28, 2012
Accepted
April 13, 2012
Jpn. J. Chemother. 60 (4): 469-477, 2012
