CASIN I, BREUIL J, PODGLAJEN I, DARCHIS JP, COLLATZ E; Interscience Conference on Antimicrobial Agents and Chemotherapy (43rd: 2003: Chicago, Ill.).
Abstr Intersci Conf Antimicrob Agents Chemother Intersci Conf Antimicrob Agents Chemother. 2003 Sep 14-17; 43: abstract no. C1-60.
Univ. Paris, Paris, France.
BACKGROUND: While HLR-Cip was fast to occur in E. coli and other Enterobacteriaceae, it seems exceptional in Salmonellae. Following the isolation of S. Typhimurium (STm) strains with HLR-Cip (MIC=32 microg/ml) from infected patients in France, we attempted to reproduce this phenotype in vitro in order to identify the mutational steps necessary for HLR-Cip acquisition in Salmonellae. METHODS: Two STm strains (phage type DT104 [NalS] and DT408 [NalR]) and one S. Hadar (SHa, NalR) were used for in vitro selection of HLR-Cip mutants. The MICs of nalidixic acid, norfloxacin, Cip, and chloramphenicol, in the absence or presence (50 microg/ml) of the efflux pump inhibitor Phe-Arg-b -naphthylamide were determined. The doubling times of the mutants were estimated.. The nucleotide sequences of the quinolone resistance determining regions of gyrA, gyrB, parC and parE and of marROA were determined. RESULTS: The STm DT408 strain accumulated five topopisomerase mutations (Gyr A:Ser83Phe, Asp87Gly; Gyr B:Ser464Phe; Par C:Ser80Cys, Glu84Lys;), the DT104 strain four (gyr A:Ser83Tyr, Asp87Tyr; gyr B:Ser464Phe; par C:Ser80Arg) and the SHa strain four (gyr A:Ser83Phe, Asp87Asn; gyr B:Phe462Ile, Ser464Phe) entailing MICs of Cip of 64, 32 and 32 microg/ml, respectively. In each case, there was an early mutational step which did not concern the topoisomerases and an additional step engendering growth defects (small colonies; @ two-fold increase in doubling time). However, no apparent growth defects persisted in the final-step HLR-Cip mutants. Drug efflux occurred in the intermediate-step, low-level Cip-resistant mutants (MIC =4 microg/ml). No mutations were observed in marROA. CONCLUSIONS: The multi-step selection of Salmonella HLR-Cip mutants in vitro involves phenotypic suppression of mutation(s) affecting their growth characteristics. It is conceivable that a similar process has occurred in as yet rare HLR-Cip clinical isolates.
Publication Types:
Keywords:
- Base Sequence
- Ciprofloxacin
- France
- Humans
- In Vitro
- Microbial Sensitivity Tests
- Mutation
- Nalidixic Acid
- Norfloxacin
- Salmonella
- Salmonella Infections
- Salmonella Phages
- Selection (Genetics)
- genetics
Other ID:
UI: 102265113
From Meeting Abstracts