Abstract
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. 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. 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. 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.
Highlights
IntroductionBacterial resistance could be caused by horizontal gene transfer, recombination processes and by genome mutation
The necessity to retain the efficiency of antibiotics and curtail the expansion of antibiotic resistance has already overwhelmed the scope of health care systems and has become a serious socioeconomic problem.Bacterial resistance could be caused by horizontal gene transfer, recombination processes and by genome mutation
According to National Antimicrobial Susceptibility Program[24], ciprofloxacin susceptibility limit for Salmonella Typhimurium is 4 μg.mL-1, and bacteria which grow in the presence of ciprofloxacin in these and higher concentration are considered to be resistant
Summary
Bacterial resistance could be caused by horizontal gene transfer, recombination processes and by genome mutation. Chromosomal mutations can lead to antibiotic resistance in several different ways. Much attention has been given to the idea that the mutation process in bacterial populations is not a static event but a complex network of factors influencing the rate and the type of mutants[1]. Different stresses such as starvation, oxidation or UV irradiation can increase the mutation rates of bacteria[2]. Pathogenic bacteria are exposed to different chemical and physical agents which may damage DNA resulting in mutations
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