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Abstract
Treatment of Escherichia coli with sub-inhibitory levels of valine has been observed to confer kanamycin resistance; however, the role of catalase in this resistance is unknown. In this study, the role of catalase activity in increased resistance to kanamycin due to valine-induced amino acid starvation was investigated. E. coli K-12 wildtype strain and mutants Δ kat E, Δ kat G, and Δ kat E/Δ kat G were used to assess kanamycin resistance after their corresponding deletions were validated by PCR. Once starved using an excess of valine, growth was monitored by turbidity and catalase activity was measured by a floating disc assay. Antibiotic resistance was assessed using transient antibiotic resistance assays and minimum inhibitory concentration tests. Valine-induced amino acid starvation resulted in short-term antibiotic resistance, but did not confer long-term resistance. Comparing the adaptive resistance between the wild-type, Δ kat E, Δ kat G, and Δ kat E/Δ kat G strains as assessed by transient resistance assay and minimum inhibitory concentration, no loss in adaptive resistance was observed in any deletion mutant. The catalase activity measured by floating disc assay showed no difference between the control and starved cultures; however, the WT and Δ kat G had significantly higher catalase activity compared to Δ kat E, while Δ kat E/Δ kat G had no activity. Taken together, these findings suggest the catalases encoded by kat E and kat G were not responsible for conferring the short-term adaptive kanamycin resistance.