Antibiotic Tolerance in Escherichia coli under Stringent Response Correlates to Increased Catalase Activity

Bactericidal antibiotics are known to induce bacterial cell death through the production of reactive oxygen species, which can be neutralized by bacterial oxidative stress control proteins such as catalases. In Escherichia coli, the katE gene encoding catalase is induced by the stringent response pathway. Stringent response is often activated under nutrient and amino acid starvation such as isoleucine deficiency. This study examines stringent response mediated catalase production and its role in antibiotic tolerance. In E. coli K-12, and the K-12 deletion mutant rel A and double deletion mutant rel A and spo T, isoleucine starvation was achieved by incubation with excess valine. Catalase production was examined through a floating disk assay, while susceptibility to kanamycin was determined through a bacterial killing assay as well as a XTT viability assay. Results showed that under starved conditions, wild-type E. coli had higher catalase production as well as kanamycin tolerance compared to the mutant strains.