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.

Group A rotaviruses (RVAs) are major enteric pathogens causing infections in calves. To investigate the epidemiological characteristics and genetic diversity of bovine rotavirus (BRV), 233 fecal samples were collected from calves with diarrhea in northeast China. The samples were analyzed for sequences encoding the inner capsid protein VP6 (subgroup) and the outer capsid proteins VP7 and VP4 (G and P type, respectively) using RT-PCR. Ten of the 233 samples (4.3%) were identified as BRV positive and were used for virus isolation and sequence analysis, revealing that all strains analyzed were of the G6P[1] genotype. The isolates exhibited high VP6 sequence identity to the USA cow RVA NCDV strain (>99% amino acid identity) and were further shown to be closely related to Japanese cow RVA BRV101 and Israelian human RVA G6P[1] strains, with >99% amino acid identity to VP7 and VP4 proteins, respectively. Comparative analyses of genome-predicted amino acid sequences between the isolates and the NCDV strains indicated that the antigenicity and infectivity of the strains isolated had changed. In this study, BRV genotypes and the genetic diversity among vaccinated cattle herds were monitored to provide epidemiological data and references for early diagnosis, allowing for early detection of new, potentially pathogenic RVA strains.

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.

Salmonella pullorum (S. pullorum) remains a major enteric pathogen in young chicks, causing high mortality and severe economic losses in poultry production. This study evaluated a prophylactic strategy using engineered Bacillus subtilis (B. subtilis) expressing gallus trefoil factor 2 (gTFF2) and epidermal growth factor (gEGF) to protect chicks against S. pullorum infection. In vitro, gEGF significantly promoted UMNSAH/DF-1 (DF-1) cell proliferation, whereas both gTFF2 and gEGF enhanced epithelial cell migration. In vivo, oral administration of recombinant B. subtilis significantly reduced mortality from 75.0% and 66.7% in the PBS and pHT43 groups to 50%, 33.3%, and 25.0% in the gTFF2, gEGF, and gTFF2+gEGF groups, respectively. Cecal colonization of S. pullorum was reduced by 2–4 log₁₀ CFU/g, accompanied by improved average daily gain and immune organ indices. Treatment also significantly decreased serum IL-6 levels and increased TGF-β levels (p < 0.05), indicating attenuation of the inflammatory response. Histological analysis showed significantly increased villus height (0.94–1.58-fold) and villus height-to-crypt depth ratio (1.47–3.25-fold) compared with the infected controls, together with markedly alleviated hepatic and intestinal lesions. The combined administration of gTFF2- and gEGF-expressing strains consistently exhibited the greatest protective efficacy. Collectively, these findings demonstrate that engineered probiotic-mediated delivery of mucosal repair factors represents a promising antibiotic-alternative strategy for preventing pullorum disease and improving intestinal health in poultry production.