Mastitis caused by Staphylococcus aureus (S. aureus) in dairy cows is one of the most common clinical diseases in dairy cattle. Unfortunately, traditional antibiotic treatment has resulted in the emergence of drug-resistant strains of bacteria, making this disease more difficult to treat. Therefore, novel lipopeptide antibiotics are becoming increasingly important in treating bacterial diseases, and developing novel antibiotics is critical in controlling mastitis in dairy cows. We designed and synthesized three cationic lipopeptides with palmitic acid, all with two positive charges and dextral amino acids. The lipopeptides’ antibacterial activity against S. aureus was determined using MIC and scanning electron microscopy. The safety concentration range of lipopeptides for clinical usage was then estimated using the mouse erythrocyte hemolysis assay and CCK8 cytotoxicity. Finally, lipopeptides with high antibacterial activity and minimal cytotoxicity were selected for the treatment experiments regarding mastitis in mice. The observation of histopathological changes, bacterial tissue load and expression of inflammatory factors determined the therapeutic effects of lipopeptides on mastitis in mice. The results showed that all three lipopeptides displayed some antibacterial activity against S. aureus, with C16dKdK having a strong antibacterial impact and being able to treat the mastitis induced by S. aureus infection in mice within a safe concentration range. The findings of this study can be used as a starting point for the development of new medications for the treatment of mastitis in dairy cows.

Streptococcus equi subsp. zooepidemicus (SEZ) ATCC35246 can invade the brain and cause severe neutrophils infiltration in brain tissue. This microorganism can survive and reproduce to an extremely high CFU burden (10⁸–10⁹/organ) under stressful neutrophils infiltration circumstances. The aim of this research is to explore the mechanism of the SEZ hypervirulent strain with its specific bifA gene which avoids being eliminated by neutrophils in the brain. We isolated the primary mouse neutrophils to treat SEZ WT and bifA gene defective (ΔBif) strains. The ΔBif strain had a weakened function of defending against neutrophils killing in vitro. The interaction between BifA and ezrin proteins in neutrophils were identified by co-IP and immunoblot. In neutrophils, the BifA interacts with ezrin and triggers the phosphorylation of ezrin at its Thr567 site in a PKC-dependent manner, then the excessive elevation of phosphorylated-ezrin recruits Dbl and activates Rac1. Since the Rac1 is closely relevant to several critical cellular functions, its abnormal activation will lead to neutrophils dysfunction and benefit to SEZ survival from neutrophils killing. Our findings reveal a novel consequence of BifA and ERM family protein (for ezrin, radixin, moesin) interaction, which happens between BifA and ezrin in neutrophils and contributes to SEZ survival in the brain. BifA should be considered as a potential target for drug development to prevent SEZ infection.

Bovine and ovine respiratory diseases are commonly associated with multiple bacterial pathogens, including Mycoplasma bovis (Mb), Mycoplasma ovipneumoniae (Mo), Mannheimia haemolytica (Mh), Pasteurella multocida (Pm), and Mycobacterium bovis (Tb). Among these, Mb and Mo are the primary causative agents of mycoplasma pneumonia in cattle and sheep, respectively. Based on this difference, two multiplex PCR assays were developed for the detection of bacterial respiratory pathogens in cattle and sheep, differing mainly in the primers targeting Mycoplasma spp. The bovine assay simultaneously detected Mb, Mh, Pm, and Tb, while the ovine assay detected Mo, Mh, Pm, and Tb, with expected amplicon sizes of 319/320 bp, 390 bp, 528 bp, and 274 bp. After optimization, both assays were able to simultaneously detect the target pathogens and showed good specificity, sensitivity, and reproducibility, with detection limits of 1.0 × 10³ copies/μL for the bovine assay and 1.0 × 10²–10³ copies/μL for the ovine assay. Preliminary testing using clinical samples demonstrated that the assays could detect the target bacterial pathogens. These results indicate that the developed multiplex PCR assays provide a basis for further validation and potential application in the detection of bacterial respiratory pathogens in cattle and sheep.

Streptococcus agalactiae (S. agalactiae), also known as Group B Streptococcus (GBS), is an important zoonotic pathogen. It is an important pathogen that causes bovine mastitis and can also lead to severe infections in newborns, pregnant women, and individuals with a weakened immune system. Adhesion to host cells is the first critical step in S. agalactiae infection, making the identification of key adhesion-related genes essential for understanding the pathogenic mechanisms of GBS. In this study, we used the Tn transposon system to construct a mutant library of S. agalactiae A909 and employed the mouse mammary epithelial cell line EPH4-Ev as a model to screen and validate adhesion-related genes. Our results revealed a gene cluster containing BP, AP1, and SrtC. While these genes did not affect the basic biological characteristics of the bacteria, they significantly influenced the adhesion rate to cells and the virulence of A909 in mice. Further transcriptomic analysis revealed that the Tnfsf15 gene plays a critical role in the regulation of A909 strain pathogenicity mediated by the BP, AP1, and SrtC gene clusters during host infection.