Efficacy of a serogroup O9 vaccine.

There are currently no approved vaccines against the opportunistic pathogen . Among vaccine targets, the lipopolysaccharide (LPS) O antigen of is the most immunodominant protective candidate. There are 20 different O antigens composed of different repeat sugar structures conferring serogroup specificity, and 10 are found most frequently in infection. Thus, one approach to combat infection by could be to generate immunity with a vaccine cocktail that includes all these serogroups. Serogroup O9 is 1 of the 10 serogroups commonly found in infection, but it has never been developed into a vaccine, due in part to the acid-labile nature of the O9 polysaccharide. Our laboratory has previously shown that intranasal administration of an attenuated strain expressing the serogroup O11 LPS O antigen was effective in clearing bacteria and preventing mortality in mice following intranasal challenge with serogroup O11 . Consequently, we set out to develop a serogroup O9 vaccine using a similar approach. Here, we show that expressing serogroup O9 triggered an antibody-mediated immune response following intranasal administration to mice and that it conferred protection from serogroup O9 in a murine model of acute pneumonia.