Killed whole-cell Staphylococcus aureus formulation in Montanide ISA266 and Alum adjuvants: different vaccine formulations varied in the vaccine's potency and efficacy.

Immunotherapy can be a sensible alternative because invasive Staphylococcus aureus infection mortality, morbidity, and cost are still alarmingly high despite the development of multiple new medications to treat methicillin-resistant S. aureus infections. Herein, killed whole-cell Staphylococcus aureus was formulated in Montanide ISA266 and Alum adjuvants, and the potency and efficacy of the vaccine were studied. After the preparation of two kinds of whole-cell vaccine (bacterin and lysate), 20 µg of each vaccine candidate was formulated in Montanide ISA266 and Alum adjuvants, then subcutaneously injected in distinct groups. Blood samples were taken two weeks after each booster injection, and two booster shots were given at 2-week intervals. Sera were examined by ELISA for total IgG, isotypes (IgG1 and IgG2a), and cytokine production (IFN-γ and IL-4), respectively, to ascertain the kind of induced immune response. Experimental mice were challenged intraperitoneally with 5 × 108 CFU of bacteria 2 weeks after their last immunization, and the mortality rate and bacterial load were measured. Both immunogens elicited strong humoral immune responses, producing antibodies that improved opsonic capability, IFN-γ, and IL-4 production and protectivity in response to the experimental challenge. Compared to other immunized groups, the lysate formulation with Montanide ISA266 produced a greater antibody titer and IgG1 isotype and showed the highest vaccine potency. Additionally, combining the whole-cell vaccine (bacterin and lysate) with the adjuvant Montanide ISA266 increased IFN-γ and IL-4 cytokines response and protection in the experimental challenge. These findings show that avoiding S. aureus infection using active vaccination with inactivated whole-cell vaccines (bacterin and lysate) may be a successful strategy. The type of adjuvant in the vaccine formulation is important and influences vaccine potency and efficacy.