Comparative immunogenicity and protective efficacy of formaldehyde-inactivated whole-cell and sonicated whole-cell extract vaccines against multidrug-resistant Pseudomonas aeruginosa in mice

Background: Pseudomonas aeruginosa is a major opportunistic Gram-negative pathogen responsible for healthcare-associated infections, while increasing antimicrobial resistance has narrowed therapeutic options. Vaccine development therefore represents an important complementary strategy for prevention. This study compared the immunogenicity and protective efficacy of a formaldehyde-inactivated whole-cell vaccine with a sonicated whole cell extract preparation against multidrug-resistant (MDR) P. aeruginosa in mouse model. Methods: Clinical P. aeruginosa isolates were obtained from specimens collected at Dhaka Medical College Hospital between July 2022 and February 2026. Formaldehyde-inactivated whole-cell and sonicated whole cell extract preparations were produced from P. aeruginosa. A total of 144 female Swiss albino mice aged 6-8 weeks were used: 120 mice were allocated to two independent immunization experiments and 24 mice were used for LD50 determination. Mice received three intramuscular immunizations on days 0, 14, and 28. Antigen-specific serum IgG was assessed by enzyme-linked immunosorbent assay (ELISA), functional antibody activity was evaluated by serum bactericidal assay (SBA), and protective efficacy was assessed following lethal intraperitoneal challenge. Results: Ten isolates from MDR P. aeruginosa were selected by simple random sampling from the clinical isolates for vaccine preparation. The estimated protein concentration of the sonicated preparation was 1.872 mg/mL. Both vaccine groups developed significantly higher anti-P. aeruginosa IgG responses than the control group after immunization (p<0.001). Following lethal challenge, survival was 100% in mice receiving the formaldehyde-inactivated vaccine and 91.7% among mice receiving the sonicated preparation; no control mice survived. Between-vaccine differences in survival were not statistically significant. SBA demonstrated complement-dependent bactericidal activity in sera from both vaccinated groups, with activity detectable to a dilution of 1:32 for the whole-cell vaccine and 1:64 for the sonicated preparation. Conclusions: Both vaccine preparations elicited strong humoral responses and substantial protection against lethal MDR P. aeruginosa challenge in mice. The findings support further investigation of multicomponent P. aeruginosa vaccine strategies, although additional studies using multiple challenge strains and broader immunological endpoints are required before conclusions regarding translational efficacy can be drawn.