Capsular Polysaccharide Production in Escherichia coli K-30 Strain E69 May Increase Following Pretreatment with Tetracycline but not Polymyxin B

The group 1 capsule is an extracellular polysaccharide layer that encapsulates Escherichia coli K30 strain E69. Capsule synthesis and transport is dependent on the Wzy biosynthesis system, which is up-regulated when E. coli cells are exposed to sub-minimum inhibitory concentrations of various antibiotics. In this study, we examined the effects of pretreatment with different classes of antibiotics on capsular polysaccharide (CPS) production in E. coli strain E69. We hypothesized that membrane-disrupting antibiotics like polymyxin B would cause greater osmotic stress and hence a greater increase in CPS production relative to antibiotics like tetracycline that disrupt protein synthesis. Subinhibitory concentrations of tetracycline and polymyxin B were used to pretreat strain E69 and E. coli strain CWG655Δ[wza-wzb-wzcK30], which lacks 3 genes belonging to the Wzy system. Following pretreatment, CPS was extracted and quantified using the phenol sulphuric acid colourimetric assay. We observed that tetracycline exposure led to increased CPS production in E69 while polymyxin B exposure did not. Our preliminary data suggest that CPS production does not increase following pretreatment with antibiotics that disrupt the outer membrane but increases following pretreatment with antibiotics that inhibit translation. This study adds to our knowledge of factors that may contribute to bacterial resistance to antibiotics.