RT Journal Article SR Electronic(1) A1 Giraud, Etienne A1 Cloeckaert, Axel A1 Baucheron, Sylvie A1 Mouline, Christian A1 Chaslus-Dancla, ElisabethYR 2003 T1 Fitness cost of fluoroquinolone resistance in Salmonella enterica serovar Typhimurium JF Journal of Medical Microbiology, VO 52 IS 8 SP 697 OP 703 DO https://doi.org/10.1099/jmm.0.05178-0 PB Microbiology Society, SN 1473-5644, AB High-level fluoroquinolone (FQ) resistance is still infrequent in salmonellae, compared with other pathogenic enterobacteria. Data provided in this work support the hypothesis that the mechanisms that confer high-level FQ resistance on salmonellae have a prohibitive fitness cost and may thus limit the emergence of highly resistant clones. In vitro mutants that were highly resistant to ciprofloxacin (MIC = 8 and 16 μg ml−1) showed generation times 1.4- and 2-fold longer than their parent strains and were unable to colonize the gut of chickens. Electron microscopy showed an altered morphology for one of these mutants grown to stationary phase. Mutants selected in vivo and exhibiting intermediate resistance to ciprofloxacin (MIC = 2 μg ml−1) also showed growth defects on solid media but had normal generation times in liquid culture and colonized the gut of chickens. After in vitro or in vivo passage in the absence of antibiotic selective pressure, partial reversals of the fitness cost were observed, which were associated with slight decreases in resistance to quinolones and other unrelated antibiotics, but were not linked to the loss of gyrA mutations., UL https://www.microbiologyresearch.org/content/journal/jmm/10.1099/jmm.0.05178-0