Stringent Response Changes Cell Membrane Permeability in Escherichia coli but does not Develop Cross Tolerance to Kanamycin, Tetracycline and Ampicillin

Abstract

Stringent response induces many changes in the cell to provide a survival advantage in conditions of nutrient starvation. One of these changes is decreased susceptibility to kanamycin, tetracycline and ampicillin. In this study, we investigated changes in Escherichia coli membrane permeability induced by stringency to determine whether or not it would cause antibiotic resistance. Stringency was induced by addition of excessive valine. Phenol sulfuric carbohydrate quantification assay was used to measure changes in -/- carbohydrate concentration after incubation with E. coli wild type and rel after induction of stringency. A killing assay using 4x MIC of kanamycin, ampicillin and tetracycline after stringency induction was to determine if resistance was developed. Uptake of 2-deoxy-Dglucose was reduced while uptake of sucrose and dextran increased in wild type when -/- compared with rel mutant. Thus it suggests a decrease in permeability in plasma membrane while increasing permeability of the outer membrane. Antibiotic tolerance did not develop after 24 incubation under stringent response with either ampicillin, kanamycin or tetracycline as determined by a killing assay. Thus stringency is not sufficient to develop antibiotic cross resistance.