Negative Stain Electron Microscopic Analysis Suggests O Antigen Expression in Escherichia coli strain K-12 May Prevent T4 Interactions with the Bacterial Surface

Expression of O16 antigen on the surface of Escherichia coli K-12 has been shown to confer resistance to bacteriophage T4-mediated lysis, however, the underlying mechanism of resistance is poorly understood. In this study, we investigated a potential bacteriophage resistance mechanism using the Escherichia coli K-12 substrains DFB1655 L9, which expresses the O16 antigen, along with the isogenic substrain MG1655 which does not. We hypothesize that O16 antigen expression may confer resistance by preventing T4 from accessing cell surface receptors, thereby inhibiting adsorption. We infected both MG1655 and DFB1655 L9 with T4 phage and fixed the cells for visualization by negative stain electron microscopy. We identified bacteriophage interacting with the outer membrane of MG1655, however, none were detected on DFB1655 L9. This finding suggests that O16 antigen may confer resistance by preventing bacteriophage T4 from interacting with the DFB1655 L9 cell surface. Furthermore, these results contribute to existing research on how O antigen serotypes can confer resistance to phage infection.