<i>Vibrio cholerae</i> serotype impacts pathogenicity

The O1 serogroup of <i>Vibrio cholerae</i> has caused all cholera pandemics and for over a century <i>V. cholerae</i> O1 outbreak strains have been characterized by their serotype. The two <i>V. cholerae</i> serotypes differ by the presence (Ogawa) or absence (Inaba) of methylation of the terminal sugar on the lipopolysaccharide O1-antigen. Serotype switching often occurs during epidemics and has historically been attributed to the pathogen adapting to immune pressures. Here we address the impact of serotype on <i>V. cholerae</i> pathogenicity using otherwise isogenic Ogawa and Inaba versions of several clinical <i>V. cholerae</i> O1 isolates. Our findings indicate that O1 antigen methylation in Ogawa strains promotes <i>V. cholerae</i> colonization, infectivity and resistance to antimicrobial peptides. We propose that methylation of the O1 antigen elevates colonization by shielding the bacterium from cationic antimicrobial peptides at the pH of the small intestine. These observations provide insights into the biological significance of the <i>V. cholerae</i> O1 serotypes.