Deletions in the capsular polysaccharide wzy Cassette Genes differentially affect susceptibility to Nitrofurantoin in Escherichia coli K-12 compared to Escherichia coli K30

Abstract

The wzy cassette is a set of genes responsible for capsular polysaccharide and exopolysaccharide polymerization and export. It has been shown that knockouts of the wzy cassette in Escherichia coli K30 strain increases susceptibility to the antibiotic nitrofurantoin, but a similar effect has not been observed in E. coli K-12. Based on this, we hypothesized that deletion of genes within the wzy cassette would change the susceptibility to nitrofurantoin differentially in E. coli K-12 compared to E. coli K30. To test this, susceptibilities to nitrofurantoin of mutants with knockouts in the wzy cassette compared to wildtypes were determined with disc diffusion assays at 28℃ and 37℃, as well as through a minimum inhibitory concentration (MIC) microtitration assay. Furthermore, the presence of capsule in all variants was determined with india ink staining to investigate the role of capsule in nitrofurantoin resistance. Our results show an increase in susceptibility to nitrofurantoin in only the E. coli K30 wzb and full wzy cassette knockouts at 37℃, but an increase in resistance in the E. coli K-12 wza knockout at 28℃. The MIC assay in liquid media showed the MIC for E. coli K30 wza was higher than the MIC of the E. coli K30 wildtype whereas the wzb and full cassette knockouts showed no change. Furthermore, capsule was only visualized in the E. coli K30 wildtype. Altogether our results suggest that the E. coli K30 and K-12 wzy cassette mutants respond differentially to nitrofurantoin and this effect occurs through a capsule-independent mechanism.