AIM: The purpose of this study was to determine how various compounds known to be positive mutagens, contribute to the development of mutations leading to ciprofloxacin resistance in Salmonella enterica subsp. enterica serotype Typhimurium. The molecular mechanism of ciprofloxacin resistance in treated strains was investigated. METHODS: A modified version of the incorporation plate test was used for quantitative determination of ciprofloxacin resistant mutants and for assessment of the mutation frequency induced by the positive mutagens in different concentrations. An AS-PCR-RFLP for monitoring of gyrA mutations was applied. RESULTS: Mutation frequency, expressed as number of antibiotic resistant colonies per 10(8) viable cells, was much higher after exposure of bacterial cells to 3-(5-nitro-2-furyl) acrylic acid and 2-nitrofluorene. All isolated cultures retain decreased susceptibility to antibiotic after multiple passages in antibiotic-free medium. 2-nitrofluorene was the best inducer of mutations in gyrA and in regulation genes affecting suppression of synthesis of outer membrane porins. 3-(5-nitro-2-furyl) acrylic acid gives rise to overproduction of efflux pump. CONCLUSIONS: The data suggest that antibiotic resistance may not be only a consequence of misuse of antibiotics. A polluted environment as well as food processing could contribute to this unwanted process.

Department of Nutrition and Food Assessment Faculty of Chemical and Food Technology Slovak University of Technology Bratislava Slovak Republic

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