Protection against Experimental Melioidosis following Immunization with Live Burkholderia thailandensis Expressing amanno-Heptose Capsule

Melioidosis is a severe infectious disease caused byBurkholderia pseudomallei. It is highly resistant to antibiotic treatment, and there is currently no licensed vaccine.Burkholderia thailandensisis a close relative ofBurkholderia pseudomalleibut is essentially avirulent in mammals. In this report, we detail the protective efficacy of immunization with liveB. thailandensisE555, a strain which has been shown to express an antigenic capsule similar to that ofB. pseudomallei. Immunization with E555 induced significant protection against a lethal intraperitonealB. pseudomalleichallenge in a mouse model of infection, with no mice succumbing to infection over the course of the study, even with challenges of up to 6,000 median lethal doses. By comparison, mice immunized withB. thailandensisnot expressing aB. pseudomallei-like capsule had significantly decreased levels of protection. E555-immunized mice had significantly higher levels of IgG than mice immunized with noncapsulatedB. thailandensis, and these antibody responses were primarily directed against the capsule.