Journal Article

Mutant prevention concentrations of ciprofloxacin and enrofloxacin for <i>Salmonella enterica</i>

L. P. Randall, S. W. Cooles, L. J. V. Piddock and M. J. Woodward

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 54, issue 3, pages 688-691
Published in print September 2004 | ISSN: 0305-7453
Published online September 2004 | e-ISSN: 1460-2091 | DOI:
Mutant prevention concentrations of ciprofloxacin and enrofloxacin for Salmonella enterica

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Objectives: To determine the mutant prevention concentrations (MPCs) of ciprofloxacin and enrofloxacin against four strains of Salmonella enterica serovar Enteritidis and four strains of S. Typhimurium including one fully susceptible, one multiply resistant (MAR), one GyrA mutant and one GyrA/MAR mutant. Further, to examine mutants arising after exposure to sub-MPC concentrations of the antibiotics for susceptibility to ciprofloxacin and enrofloxacin, and cyclohexane tolerance.

Methods: MICs were determined using the agar dilution method of the BSAC. The MPC was recorded as the lowest concentration of antibiotic to inhibit growth from an inoculum of 1010 cfu.

Results: The MPCs and resulting MPC/MIC ratios of enrofloxacin were generally two- to four-fold higher than for ciprofloxacin. At 24 h for both antibiotics, MPCs were lowest for the fully susceptible strains (0.25–0.5 mg/L), similar for the MAR (1–4 mg/L) and GyrA (2–4 mg/L) mutants and highest for the GyrA/MAR mutants (1–8 mg/L). MPC/MIC ratios at 24 h were 2–16 for all strains except those for the MAR strains without mutation in gyrA where the ratios were 8–64.

Conclusions: The ability to eradicate Salmonella in vivo depends on many factors such as antibiotic susceptibility of the strain, dose and route of administration. It is suggested that these MPC values will be useful when considering dosing strategies. In view of the high MPC/MIC ratio, MAR strains with wild-type gyrA, although susceptible to ciprofloxacin (MICs 0.06–0.13 mg/L), may give rise to treatment failures.

Keywords: antibiotic resistance; cyclohexane; MAR; Typhimurium

Journal Article.  1985 words. 

Subjects: Medical Oncology ; Critical Care

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