The primary aim of this study was to evaluate the efficacy of phage against mastitis induced by drug-resistant S. aureus in a mouse model. In this study, five S. aureus phages—4086-1, 4086-2, 4086-3, 4086-4, and 4086-6—were isolated from milk samples secreted by mastitis cows. Transmission electron microscopy showed that all the five phages had icosahedral heads and short non-contractile tails, which are typical characteristics of the family Podoviridae. All these phages were species-specific against S. aureus. The one-step growth curve showed a short latency period (10–20 min) and high burst size (up to 400 PFU/infected cell). To evaluate the effectiveness of the phage 4086-1 in the treatment against mastitis, a mouse model of mastitis was challenged with drug-resistant S. aureus. The results showed the proliferation of S. aureus in the mammary glands was significantly inhibited after treating by phage 4086-1. The concentrations of TNF-α and IL-6 decreased significantly, which demonstrated the phages could effectively alleviate the inflammatory responses. Furthermore, the histopathological analysis showed that inflammatory infiltration in the mammary glands was significantly reduced. These results demonstrate that phage may be a promising alternative therapy against mastitis caused by drug-resistant S. aureus.

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Porcine circovirus type 2 (PCV2) causes many diseases in weaned piglets, leading to serious economic losses to the pig industry. This study investigated the immune response following oral administration of Lactobacillus casei ATCC393 (L. casei 393) expressing PCV2 capsid protein (Cap) fusion with the Escherichia coli heat-labile toxin B subunit (LTB) in mice. Recombinant L. casei strains were constructed using plasmids pPG611.1 and pPG612.1. The expression and localization of proteins from recombinant pPG611.1-Cap-LTB (pPG-1-Cap-LTB)/L. casei 393 and pPG612.1-Cap-LTB (pPG-2-Cap-LTB)/L. casei 393 were detected. All recombinant strains were found to be immunogenic by oral administration in mice and developed mucosal and systemic immune responses against PCV2. The titers of specific antibodies in mice administered pPG-2-Cap-LTB/L. casei 393 were higher than those in mice administered pPG-1-Cap-LTB/L. casei 393 in serum and the mucosal samples. The mucosal immune response was not only limited to the gastrointestinal tract but was also generated in other mucosal parts. Thus, the application of recombinant L. casei could aid in vaccine development for PCV2.