Pseudomonas aeruginosa is an opportunistic nosocomial pathogen that causes serious infections in the respiratory tract of immunocompromised or critically ill patients, and it is also a significant source of bacteremia. Treatment of these infections can be complicated due to the emergence of multidrug-resistant P. aeruginosa strains worldwide. Hence, the development of prophylactic vaccines is a priority for at-risk patients. We have previously developed a vaccine candidate with a single auxotrophy for D-glutamate, PAO1 ΔmurI, which protects against sepsis and acute pneumonia caused by P. aeruginosa. Given the paramount importance of safety in the development of live attenuated vaccines, we have improved the safety of the vaccine candidate by reducing the probability of a reversion to virulence by the inclusion of an additional auxotrophy for D-alanine. Single and double auxotrophs behaved in a similar manner in relation to the attenuation level, immunogenicity and protective efficacy, but the double auxotroph has the advantage of being more stable and safer as a candidate vaccine against respiratory infections caused by P. aeruginosa.
Keywords: Pseudomonas aeruginosa; alanine racemase gene; auxotrophy; glutamate racemase gene; intranasal immunization; live-attenuated vaccine.