Role of ciprofloxacin in its synergistic effect with fosfomycin on drug-resistant strains of Pseudomonas aeruginosa.
BACKGROUND
The aim of this study was to investigate the synergistic effect of ciprofloxacin (CPFX) and fosfomycin (FOM) on CPFX-resistant Pseudomonas aeruginosa strains.


METHODS
The synergistic effect was evaluated using the fractional inhibitory concentration index, acute bactericidal effect and morphological observation.


RESULTS
In the fractional inhibitory concentration index experiments, the combination of CPFX with FOM showed a synergistic effect in 20 of 74 (27.0%) strains of P. aeruginosa. From the morphological observations, it was determined that CPFX affected the outer membrane structure. CPFX combined with FOM caused striking morphological changes, resulting in bacteriolysis. A time lag experiment suggested that the addition of CPFX prior to FOM produced more pronounced bactericidal activity than the addition of FOM prior to CPFX.


CONCLUSIONS
These results indicate that the combination of CPFX with FOM induces a synergistic effect on CPFX-resistant P. aeruginosa strains. The role of CPFX is thought to be related to damage of the outer membrane, enhancing FOM penetration.
Yamada
Sakuo
S
Department of Microbiology, Kawasaki Medical School, Okayama, Japan.
Hyo
Yukiyoshi
Y
Ohmori
Sachiyo
S
Ohuchi
Masanobu
M
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002939:Ciprofloxacin / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D004357:Drug Synergism; D005578:Fosfomycin / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D046529:Microscopy, Electron, Transmission; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000254:growth & development / Q000648:ultrastructure
D000900:Anti-Bacterial Agents; D005578:Fosfomycin; D002939:Ciprofloxacin