Increased Antibiotic Resistance Post-exposure to Sub-inhibitory Concentrations is Independent of Capsular Polysaccharide Production in Escherichia coli

Previous experiments have shown that pretreatment of Escherichia coli with sub-lethal doses of antibiotic resulted in a measurable increase in capsule production and resistance upon secondary exposure. Whether this increase in capsule was directly implicated in antibiotic resistance had been investigated by numerous papers, but conclusive evidence supporting a link has yet to be found. In this study the use of E. coli lon and rcsB genetic mutants, which over and under produce the capsular polysaccharide colanic acid respectively were utilized to mimic capsule overproduction and deficiency; colanic acid being a constituent of capsule. We investigated the role of capsular polysaccharide production in antibiotic resistance by measuring changes in turbidity as a measure of growth. Despite the lon strain having displayed both a microscopically and macroscopically observable increase in capsule production, there was no discernible difference in turbidity increase between it and the down-regulated strain in the presence of varying concentrations of kanamycin or streptomycin. Our data support the conclusion that antibiotic pretreatment independently induces both increased antibiotic resistance and capsular polysaccharide production.