Abstract
The aim of this study was to investigate the influence of 20-hydroxyecdysone (20E) on the susceptibility of growing Escherichia coli to antibiotics. Susceptibility of E.coli to antibiotics in the presence of 20E was estimated by determination of the colony-forming ability and the specific growth rate. Pretreatment with 20E decreased the bactericidal effect of ciprofloxacin (0·3 and 3·0μgml-1 ), streptomycin (10 and 40μgml-1 ) and kanamycin (10μgml-1 ) and increased the bactericidal action of 0·03μgml-1 ciprofloxacin. To study the influence of 20E on gene expression, we used strains of E.coli carrying fusions of promoters of relevant genes with the structural gene of β-galactosidase. 20E had no marked effect on the expression of antioxidant genes katG, katE, sodA and the rpoS gene (general stress response), while it (alone or combined with ciprofloxacin) markedly stimulated expression of the sulA gene belonging to the SOS regulon (DNA damage response). In growing E.coli, 20E modulated the bactericidal action of antibiotics and stimulated the SOS response. The results of this study may be used to enhance the efficiency of antibacterial therapies.
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