Deletion of the capsule phosphatase gene wzb renders Escherichia coli strain K30 sensitive to the antibiotic nitrofurantoin.

SUMMARY The group I capsular polysaccharides (CPS) are assembled through the Wzy-dependent pathway that involves Wza, Wzb and Wzc proteins. CPS has been characterized as a virulence factor that confers antimicrobial resistance in Escherichia coli (E. coli). Increasing antimicrobial resistance among uropathogens has led to increased interest in using the antibiotic nitrofurantoin. While previous studies have investigated the effect of single gene deletions of wza, wzb, and wzc on erythromycin sensitivity in E. coli K30, susceptibility of these individual gene knockout strains to nitrofurantoin has not yet been explored. We aimed to investigate the relationship between nitrofurantoin sensitivity and E. coli group I CPS production by studying its biosynthesis genes wza and wzb. Strains were confirmed via polymerase chain reaction (PCR) and Sanger sequencing. Zones of inhibition for each strain were quantified via a disc diffusion assay, and the minimum inhibitory concentration (MIC) of nitrofurantoin for each strain was determined. Results of the disc diffusion assay revealed significant differences in zone of inhibition sizes for wza-wzb-wzc and wzb mutant strains relative to wild type (WT) E. coli K30. In contrast to the E. coli K30 wzb mutant, the BW25113 wzb mutant from the Keio collection showed less sensitivity than its WT parent strain. We conclude that other factors besides the presence of capsule may be contributing to nitrofurantoin susceptibility, and that Wzb may be involved in complex interactions with substrates that affect the activation of nitrofurantoin.