Annals of Clinical Microbiology, The official Journal of the Korean Society of Clinical Microbiology


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In Vitro Activity of Antimicrobial Combination against Multidrug-Resistant Pseudomonas aeruginosa

Original article

Annals of Clinical Microbiology (Ann Clin Microbiol) 2006 April Volume 9, Issue 1, pages 1-6

In Vitro Activity of Antimicrobial Combination against Multidrug-Resistant Pseudomonas aeruginosa

Jeongsook Yoon1, Heewon Moon2, and Miae Lee2

Labgenomics Clinical Laboratories1; and Department of Clinical Pathology22, Mokdong Hospital, College of Medicine, Ewha Womans University, Seoul, Korea


Background: Pseudomonas aeruginosafrequently causes nosocomial infection. Recently, there have been reports of infection with multidrug-resistant P. aeruginosa. The purpose of this study was to evaluate the in vitro effect of antimicrobial combination against multidrug-resistant P. aeruginosa.

Methods: Twenty isolates of imipenem and/or cefepime resistant P. aeruginosa were collected from the microbiology laboratory of Ewha Womans Unversity Mokdong Hospital. Checkerboard titration method was used to assess the activity of ceftazidime or cefepime in combination with amikacin, gentamicin or aztreonam, and colistin in combination with ceftazidime or rifampin.

Results: All isolates were resistant to more than 12 antimicrobial agents including imipenem and/ or cefepime by broth microdilution method; however, no isolates were resistant to colistin. Most of the isolates showed high level resistance to ceftazidime, cefepime and meropenem, with MIC90 of 128, 512 and 64 μg/mL, respectively. The MIC90 of colistin was 2 μg/mL, which is within the susceptible range. Synergistic effect was not detected by the checkerboard titration method with any antimicrobial combinations. However, a partial synergy was observed in 40% of the isolates with the combination of ceftazidime and amikacin, 65% with ceftazidime and gentamicin, 45% with cefepime and amikacin, and 75% with cefepime and gentamicin. Other antimicrobial combinations showed indifference against most strains, and antagonism was not observed.

Conclusion: Multidrug-resistant P. aeruginosa isolates were all susceptible to colistin. The combined regimens of ceftazidime with amikacin or gentamicin and cefepime with amikacin or gentamicin revealed a partially synergistic effect in 40-75% of the isolates.

(Korean J Clin Microbiol 2006;9(1):1-6)


Pseudomonas aeruginosa, Antimicrobial combination, Synergy