In vitro activities of various antibiotics, alone and in combination with colistin methanesulfonate, against Pseudomonas aeruginosa strains isolated from cystic fibrosis patients.
BACKGROUND
The in vitro activities of various antibiotics, either alone or in combination with colistin methanesulfonate, were assessed using Pseudomonas aeruginosa strains isolated from cystic fibrosis patients.


METHODS
Except for colistin methanesulfonate, minimum inhibitory concentrations were determined by microbroth dilution technique as described by the Clinical and Laboratory Standards Institute (CLSI); for colistin methanesulfonate, a modified method of the CLSI was used. Minimum bactericidal concentrations were determined as described by the CLSI. The in vitro activities of antibiotics in combination were determined by microbroth checkerboard technique, and results were interpreted by fractional inhibitory concentration index.


RESULTS
According to MIC values, 100, 98, 96 and 84% of the isolates were found susceptible to amikacin, colistin methanesulfonate, meropenem and ceftazidime, respectively. The minimum bactericidal concentrations were generally equal to or twice as high as those of the minimum inhibitory concentrations. With a fractional inhibitory concentration index of < or =0.5 as borderline, synergistic interactions were more frequent with combinations where amikacin was involved than with those with colistin methanesulfonate. No antagonism was observed.


CONCLUSIONS
The findings of this study may play a useful role in selecting the appropriate combinations when a single agent is inadequate to treat cystic fibrosis patients with P. aeruginosa infections.
Güzel
Cağla Bozkurt
CB
Department of Pharmaceutical Microbiology, Faculty of Pharmacy, Istanbul University, Istanbul, Turkey.
Gerçeker
A Alev
AA
D000900:Anti-Bacterial Agents / Q000008:administration & dosage* / Q000493:pharmacokinetics; D003091:Colistin / Q000008:administration & dosage* / Q000493:pharmacokinetics; D003550:Cystic Fibrosis / Q000188:drug therapy* / Q000382:microbiology; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects / Q000502:physiology; D004359:Drug Therapy, Combination; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D011552:Pseudomonas Infections / Q000188:drug therapy* / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000302:isolation & purification* / Q000378:metabolism
D000900:Anti-Bacterial Agents; D003091:Colistin