ABSTRACT
E. coli exposure to ciprofloxacin disturbs cysteine homeostasis; an increase in the intracellular concentration of cysteine is dangerous due to its ability to enhance ROS generation. Unlike wild-type bacteria, in which the cysteine content did not exceed the control level, cells of the gshA mutant lacking glutathione are characterized by increased concentration of intracellular cysteine in proportion to the concentrations of the antibiotic, despite the intensive export of cysteine into the medium. At low concentrations of ciprofloxacin, the mutant strain formed half as many colonies as the parent strain in the survival test. These findings attest to the important role of the incorporation of excess cysteine into glutathione as one of the mechanisms of cysteine homeostasis during the stress response to antibiotic.
Subject(s)
Anti-Bacterial Agents , Ciprofloxacin , Cysteine , Escherichia coli , Homeostasis , Ciprofloxacin/pharmacology , Cysteine/metabolism , Escherichia coli/drug effects , Escherichia coli/genetics , Escherichia coli/metabolism , Homeostasis/drug effects , Anti-Bacterial Agents/pharmacology , Glutathione/metabolism , Escherichia coli Proteins/genetics , Escherichia coli Proteins/metabolism , Reactive Oxygen Species/metabolism , Microbial Sensitivity Tests , MutationABSTRACT
AIMS: The aim of this study was to investigate the influence of 20-hydroxyecdysone (20E) on the susceptibility of growing Escherichia coli to antibiotics. METHODS AND RESULTS: 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 3·0 µg ml-1 ), streptomycin (10 and 40 µg ml-1 ) and kanamycin (10 µg ml-1 ) and increased the bactericidal action of 0·03 µg ml-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 ß-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). CONCLUSION: In growing E. coli, 20E modulated the bactericidal action of antibiotics and stimulated the SOS response. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study may be used to enhance the efficiency of antibacterial therapies.
