Pre-treatment with Sub-Inhibitory Kanamycin Has no Effect on RpoS Expression but Increases Heat Tolerance of Escherichia coli BW25113

The RpoS sigma factor mediates the induction of the general stress response in Escherichia coli, which offers protection against a wide array of external stresses. Other studies have shown that pre-treatment of E. coli with sub-inhibitory antibiotics conferred persisting antibiotic resistance against the same and other antibiotics, and pre-treatment with high temperature also enabled resistance to low pH media. Consequently, the aim of this study was to determine whether treatment of E. coli BW25113 with sub-inhibitory kanamycin would elicit elevated RpoS expression in exponential phase cells, and subsequently result in improved survival in conditions of high temperature (50°C) and/or high acidity (pH 2). Plating was done to assess cell viability at 5, 20, and 45 minutes postincubation in stress conditions. Western blotting was used to compare RpoS expression levels of different treatments. No difference in RpoS expression was obtained between control and kanamycin treatments. Neither culture survived the pH 2 treatment in M9 minimal medium, however, after 45 minutes of treatment at high temperature, over 10-fold higher cell survival was observed in cells pre-treated with kanamycin. This indicates that sub-inhibitory kanamycin was sufficient to elicit some additional thermal resistance in E. coli, but did not induce the acidic resistance systems under the conditions tested. The involvement of RpoS in stimulating the protective response could not be concluded in this experiment.