Erysipelothrix rhusiopathiae can cause erysipelas in animals and erysipeloid in humans. Since its recurrence in 2012, swine erysipelas has caused serious losses within the pig industry in China. The aim of this study was to perform multilocus sequence typing and understand the virulence and antimicrobial susceptibility of E. rhusiopathiae isolates in China. Multilocus sequence typing (MLST) of a total of 120 strains was performed, and as a result, three different sequence types were identified, of which ST48 was the main one. Five isolates of each MLST type were randomly selected to be used to challenge mice. ST48 was associated with a higher virulence. Antimicrobial susceptibility was tested using a microdilution technique and, to analyze the resistance mechanism, six strains were selected for genome sequencing. A comparison of the six genomes indicated the presence of a suspected macrolide resistance gene, namely, Erm(A)-like, in erythromycin-resistant strains, which increased the minimum inhibitory concentration (MIC) of erythromycin against E. coli C600 at least four-fold. In addition, three mutations (gyrA86T-I, gyrA90D-N, and parC81S-I) were observed in the quinolone resistance-determining regions (QRDRs) of gyrA and parC in quinolone-resistant strains. After the gyrA gene with the 86T-I mutation or the parC gene with the 81S-I mutation was transfected into E. coli C600, the MIC of enrofloxacin against this strain increased at least two-fold. Our findings provide a theoretical basis for developing antibacterial drugs and may contribute to the clinical prevention and control of E. rhusiopathiae.

Feline calicivirus (FCV) is one of the most important pathogens causing upper respiratory tract diseases in cats, posing a serious health threat to these animals. At present, FCV is mainly prevented through vaccination, but the protective efficacy of vaccines in China is limited. In this study, based on the differences in capsid proteins of isolates from different regions in China, as reported in our previous studies, seven representative FCV epidemic strains were selected and tested for their viral titers, virulence, immunogenicity, and extensive cross-protection. Subsequently, vaccine strains were selected to prepare inactivated vaccines. The whole-genome sequencing and analysis results showed that these seven representative FCV strains and 144 reference strains fell into five groups (A, B, C, D, and E). The strains isolated in China mainly fall into groups C and D, exhibiting regional characteristics. These Chinese isolates had a distant evolutionary relationship and low homology with the current FCV-255 vaccine strain. The screened FCV-HB7 and FCV-HB10 strains displayed desirable in vitro culture characteristics, with the highest virus proliferation titers (10^9.5 TCID₅₀/mL) at 36 h post inoculation at a dose of 0.01 MOI. All five cats infected intranasally with FCV-HB7 or FCV-HB10 strains showed obvious clinical symptoms of FCV. The symptoms of cats infected with the FCV-HB7 strain were more severe than those infected with the FCV-HB10 strain. Both the single-strain inactivated immunization and combined bivalent inactivated vaccine immunization of FCV-HB7 and FCV-HB10 induced high neutralizing antibody titers in five cats immunized. Moreover, bivalent inactivated vaccine immunization protected cats from FCV-HB7 and FCV-HB10 strains. The cross-neutralizing antibody titer against seven representative FCV epidemic strains achieved by combined bivalent inactivated vaccine immunization was higher than that achieved by single-strain immunization, which was much higher than that achieved by commercial vaccine FCV-255 strain immunization. The above results suggest that the FCV-HB7 and FCV-HB10 strains screened in this study have great potential to become vaccine strains with broad-spectrum protective efficacy. However, their immune protective efficacy needs to be further verified by multiple methods before clinical application.

Introduction: Mycoplasma synoviae (MS) is a globally important avian pathogen causing infectious synovitis and respiratory diseases in poultry, leading to significant economic losses. Despite advances in vaccine development, a commercially viable subunit vaccine against MS remains elusive.Methods: We sequenced whole genomes of six clinical MS strains isolated from different Chinese provinces. Common genes were analyzed using Biopython software, identifying those with high copy numbers in virulent strains and shared among all strains. Vaxign2 and IEDB Antibody Epitope Prediction were used to analyze protein properties. We assessed immune protective effects of candidate proteins and developed a multivalent subunit vaccine.Results: Ten candidate vaccine proteins were initially selected. A multivalent subunit vaccine composed of MSPB, Ppht, Cfba, and EF-G displayed the best protective effect. The optimal immunization dosage was 20μg, with each protein accounting for 25%. The immune production period was determined to be 28 days post-first immunization, lasting 180 days. The immune protection rate against highly virulent strains reached 90%∼100%.Discussion: This study provides a new approach for screening vaccine antigens and develops an effective candidate vaccine for MS prevention. The multivalent subunit vaccine shows promising results in protecting against MS infections, potentially offering a solution to reduce economic losses in the poultry industry.

Mycoplasma synoviae (MS) infection predominantly manifests as lower respiratory symptoms but also leads to reduced egg production and increased culling rates in laying hens, causing significant economic losses throughout the production cycle. Vaccination remains the most cost-effective strategy to protect layers from MS infection. Previous studies from our laboratory identified and screened immunogenic proteins of MS, culminating in the development of a subunit vaccine that provided robust protection with a two-dose immunization. Building on these findings, this study evaluated various formulations, antigen combinations, and adjuvants of MS inactivated vaccines, tailored to meet field immunization protocols and disease prevention needs. The results indicated that an inactivated vaccine combining whole-cell and subunit components of MS offered effective protection in layers during the pullet-rearing phase with a single immunization. Interestingly, vaccine-induced antibody levels did not strongly correlate with protective efficacy, underscoring the importance of host cellular immunity in combating MS infection. In conclusion, this study addresses field-relevant challenges and presents innovative strategies for MS control in laying hens, offering practical insights for improving disease control and flock management.

Erysipelothrix rhusiopathiae is a causative agent of erysipelas in animals and erysipeloid in humans. However, current information regarding E. rhusiopathiae pathogenesis remains limited. Previously, we identified two E. rhusiopathiae strains, SE38 and G4T10, which were virulent and avirulent in pigs, respectively. Here, to further study the pathogenic mechanism of E. rhusiopathiae, we sequenced and assembled the genomes of strains SE38 and G4T10, and performed a comparative genomic analysis to identify differences or mutations in virulence-associated genes. Next, we comparatively analyzed 25 E. rhusiopathiae virulence-associated genes in SE38 and G4T10. Compared with that of SE38, the spaA gene of the G4T10 strain lacked 120 bp, encoding repeat units at the C-terminal of SpaA. To examine whether these deletions or splits influence E. rhusiopathiae virulence, these 120 bp were successfully deleted from the spaA gene in strain SE38 by homologous recombination. The mutant strain ΔspaA displayed attenuated virulence in mice and decreased adhesion to porcine iliac artery endothelial cells, which was also observed using the corresponding mutant protein SpaA’. Our results demonstrate that SpaA-mediated adhesion between E. rhusiopathiae and host cells is dependent on its C-terminal repeat units.

African swine fever virus (ASFV) antibody detection is an important component of serological surveillance and retrospective investigations. DP238L was recently identified by proteome-wide serum-antibody profiling as a frequently recognized ASFV antigen, and recombinant DP238L was further shown to react with ASFV-positive sera and to elicit antigen-specific antibody responses in immunized pigs. Here, we extend those observations toward diagnostic assay development and preliminary validation. Full-length DP238L from ASFV strain SY-1 (GenBank OM161110) was evaluated as a single recombinant coating antigen for an indirect ELISA (DP238L-iELISA). Independent sequence analysis showed that SY-1 DP238L contains 238 amino acids, with a theoretical molecular mass of 27.13 kDa, a theoretical pI of 4.92, and a GRAVY value of −0.97. In a quality-restricted subset of complete, unambiguous 238-aa homologs (n = 7), amino acid identity to SY-1 ranged from 97.48% to 100% (median, 98.74%). Recombinant DP238L was expressed and purified from Escherichia coli and specifically recognized by ASFV-positive swine serum. ELISA optimization identified a coating antigen concentration of 0.5 μg/mL, a secondary-antibody working dilution of 1:2500 (0.4 μg/mL), a serum dilution of 1:100, a serum incubation time of 45 min, and a substrate development time of 15 min. Using 518 clinical swine serum samples categorized according to the commercial INgezim PPA COMPAC K3 blocking ELISA, ROC analysis yielded an AUC of 0.9989 (bootstrap 95% CI, 0.9973–0.9999). At the selected S/P cutoff of 0.30, positive percent agreement and negative percent agreement relative to INgezim were 97.2% and 98.7%, respectively; overall agreement was 98.3% and Cohen’s $\kappa$ was 0.956. A limited six-sample heterologous panel provided preliminary cross-reactivity information, with all tested samples remaining below the cutoff. In a longitudinal panel from five experimentally infected pigs, three animals exceeded the cutoff at 7 days post-infection (dpi) and all five exceeded it by 10 dpi. These findings support DP238L as a promising recombinant antigen for ASFV serological assay development while emphasizing that the present results represent an internal comparator-based preliminary evaluation requiring broader independent validation.