Recombinant PBP2a as a vaccine candidate against methicillin-resistant Staphylococcus aureus: Immunogenicity and protectivity.

Methicillin-resistant Staphylococcus aureus infections are focal and development of an effective vaccine can help to control this infection. Here, recombinant PBP2a was studied in mouse model. Following the preparation of recombinant PBP2a, Balb/c mice were injected subcutaneously with 20 µg of r-PBP2a formulated in Freund's adjuvant three times with three weeks intervals with proper control group. Total and specific isotype antibodies were evaluated on sera by ELISA. Opsonophagocytic activity was also investigated on the sera samples. Intraperitonealchallenge with a sub-lethal dose of MRSA (5 × 108 CFU) was done in experimental mice. Following that, the number of bacteria from kidneys of experimental mice were determined. Survival rate was recorded for 60 days. Significant increase of antibody with high level of IgG1, IgG2a and IgG2b isotypes was demonstrated in vaccinated mice versus the control group (P < 0.005). The bacterial load in the kidneys from immunized mice was 1000 times less thancontrol group (PBS) and opsonophagocytic activity of immunized mice sera significantly increased (P < 0.0001). Finally the life span of immunized mice after bacterial challenge was extended versus control mice. These results may indicate the capacity of PBP2a as a candidate vaccine to control the MRSA infections.

Solubilization Behavior of Polyene Antibiotics in Nanomicellar System: Insights from Molecular Dynamics Simulation of the Amphotericin B and Nystatin Interactions with Polysorbate 80.

Amphotericin B (AmB) and Nystatin (Nys) are the drugs of choice for treatment of systemic and superficial mycotic infections, respectively, with their full clinical potential unrealized due to the lack of high therapeutic index formulations for their solubilized delivery. In the present study, using a coarse-grained (CG) molecular dynamics (MD) simulation approach, we investigated the interaction of AmB and Nys with Polysorbate 80 (P80) to gain insight into the behavior of these polyene antibiotics (PAs) in nanomicellar solution and derive potential implications for their formulation development. While the encapsulation process was predominantly governed by hydrophobic forces, the dynamics, hydration, localization, orientation, and solvation of PAs in the micelle were largely controlled by hydrophilic interactions. Simulation results rationalized the experimentally observed capability of P80 in solubilizing PAs by indicating (i) the dominant kinetics of drugs encapsulation over self-association; (ii) significantly lower hydration of the drugs at encapsulated state compared with aggregated state; (iii) monomeric solubilization of the drugs; (iv) contribution of drug-micelle interactions to the solubilization; (v) suppressed diffusivity of the encapsulated drugs; (vi) high loading capacity of the micelle; and (vii) the structural robustness of the micelle against drug loading. Supported from the experimental data, our simulations determined the preferred location of PAs to be the core-shell interface at the relatively shallow depth of 75% of micelle radius. Deeper penetration of PAs was impeded by the synergistic effects of (i) limited diffusion of water; and (ii) perpendicular orientation of these drug molecules with respect to the micelle radius. PAs were solvated almost exclusively in the aqueous poly-oxyethylene (POE) medium due to the distance-related lack of interaction with the core, explaining the documented insensitivity of Nys solubilization to drug-core compatibility in detergent micelles. Based on the obtained results, the dearth of water at interior sites of micelle and the large lateral occupation space of PAs lead to shallow insertion, broad radial distribution, and lack of core interactions of the amphiphilic drugs. Hence, controlled promotion of micelle permeability and optimization of chain crowding in palisade layer may help to achieve more efficient solubilization of the PAs.