Biofilm production in Escherichia coli K30 with group 1 capsular gene wza and wza-wzb-wzc deletions is not correlated with Erythromycin resistance phenotypes in liquid media

Abstract

The Wzy-dependent capsular polysaccharide export system consists of an outer membrane channel (Wza), inner membrane channel and tyrosine autokinase (Wzc), and regulatory phosphatase (Wzb), and is responsible for the export and assembly of extracellular polysaccharide capsules. In Escherichia coli K30, this system is critical for the formation of group 1 capsules. Previous studies have shown that E. coli K30 Δwza and Δwza-wzb-wzc have greater resistance to erythromycin, a macrolide antibiotic, on solid media compared to wild-type K30; however, the opposite phenotype was observed in liquid media. Therefore, we hypothesized that the different erythromycin resistance phenotypes in E. coli K30 wild-type, Δwza, and Δwza-wzb-wzc are due to differences in biofilm production in solid and liquid media. In this study, we investigated whether biofilm formation is correlated with the differential erythromycin resistance phenotype of wild-type E. coli K30, Δwza, and Δwza-wzb-wzc in solid and liquid media. Erythromycin disc diffusion assays on solid media, minimum inhibitory concentration assays in liquid media and crystal violet biofilm assays were performed on all three strains. We found that Δwza and Δwza-wzb-wzc were more resistant than the wild-type strain on solid media, but all three strains had similar levels of resistance in liquid media. In contrast to previous studies, we obtained consistent erythromycin MIC values in liquid media and determined that it was between 125 and 250 μg/mL, but we were unable to obtain consistent biofilm formation among our three trials. Thus, we conclude that there is no correlation between biofilm production and erythromycin resistance in E. coli K30 wild-type, Δwza, and Δwza-wzb-wzc in liquid media.