Pretreatment with Sub-minimal Inhibitory Concentration of Kanamycin Increases RpoH Levels in Escherichia coli SC122

Abstract

Pretreatment of Escherichia coli with sub-MIC of 4 µg/ml kanamycin led to an increase in cell viability and survival upon exposure to temperatures greater than 45°C. The viability of sub-MIC kanamycin pre-treated wild type E. coli SC122 and K165 (∆ rpoH ) upon transfer to 45°C was assessed using spectrophotometry and spread plating by cellular enumeration. Cellular levels of RpoH in sub-MIC treated E. coli SC122 cultures grown at 30°C were monitored using western blotting. Increase of RpoH levels was used as an indicator of a heat resistant phenotype. At 45°C, sub-MIC of kanamycin pre-treated E. coli SC122 showed a higher growth rate between 20 – 40 minutes compared to the untreated cultures. As expected, no significant changes in turbidity and a rapid drop in cell viability were observed for all treatments of the K165 strain in identical conditions. RpoH detection via western blotting in SC122 sub-MIC of kanamycin treated cultures grown at 30°C revealed an increase in band intensity, correlating to an increase in RpoH amounts over time. We reported the increase of RpoH levels in E. coli SC122 in response to sub-MIC of kanamycin.