Protective potential of microencapsulated recombinant staphylococcal enterotoxin-C in a murine staphylococcal mastitis model

Abstract Mastitis is inflammation of the mammary gland and is considered an economically important disease of the dairy industry. S. aureus is the contagious pathogen involved in both subclinical and clinical mastitis in dairy cows. Due to the hardy nature of S. aureus and the emergence of multi-drug resistant S. aureus, the chance of treatment failure in infections is relatively high. Hence, it is generally accepted that antibiotics alone cannot solve the overall therapeutic dilemma, and other treatment modalities, such as vaccines or immunotherapies, are urgently needed. Staphylococcal enterotoxin type C (SEC) is one of the most important immunogenic determinants among the different enterotoxins and is invariantly expressed by bovine isolates of S. aureus. In the present study, we examined whether recombinant staphylococcal enterotoxin C (rSEC) protein encapsulated in poly lactide-co-glycolide microparticles (PLGA) can be used for active immunization against staphylococcal mastitis in a murine model. Adult Swiss albino female mice (n = 6) were allotted into five groups for immunization in a prime-boost regimen: (1) control group (sterile PBS); (2) rSEC-PLGA group; (3) bacterin group; (4) PLGA group; and (5) rSEC group. The immunoglobulin G titre in serum was significantly (p < 0.05) higher in the PLGA-rSEC group than in the bacterin group. Furthermore, male and female mice (1:3 ratio) were cohabitated after the second immunization to ensure impregnation of the female mice for intramammary bacterial challenge. Three days postpartum, immunized lactating mice were challenged with 107 colony forming units (CFUs) of β-hemolytic coagulase positive S. aureus in the mammary ducts. The protective mechanism of PLGA-encapsulated rSEC against intramammary challenge of S. aureus was evaluated using S. aureus-specific IgG, IL-10, CRP, bacterial load and histopathology. PLGA-rSEC exhibited a strong immune response against S. aureus and could therefore be a promising vaccine candidate against S. aureus bovine mastitis.