The Effect of Sub-Inhibitory Streptomycin on Capsular Polysaccharide Production and Streptomycin Resistance in Escherichia coli

Previous studies have shown that pre-treatment of Escherichia coli B23 with subinhibitory concentrations of aminoglycosides leads to a subsequent increase in the level of capsular polysaccharide, as well as an increased resistance to streptomycin. Using capsular polysaccharide synthesis pathway mutants, we investigated the correlation between the level of capsular polysaccharide and streptomycin resistance. Antibiotic resistance was measured by minimum inhibitory concentration. Capsular polysaccharide was isolated and quantified via an anthrone carbohydrate assay. After pretreatment with 2 μg/ml of streptomycin, E. coli strains B23 and up-regulated capsule strain JW0429-1 showed increased levels of capsule polysaccharide, while the mutant parental strain BW25113 and the down-regulated capsule strain JW2205-2 showed decreased levels of capsule. We did not observe an increased level of resistance in any of the 4 strains following treatment and could not confirm the previously reported effect on the B23 strain. We propose that an increased production of capsule has little effect on streptomycin resistance in E. coli. The differences in resistance and capsule production with streptomycin treatment may be due to different mechanisms of response in the strains.