Riemerella anatipestifer (R. anatipestifer) can cause serositis in multiple poultry species, resulting in significant losses. Although R. anatipestifer-caused infections in ducks have been well established, the literature about this disease in geese is rare. Here, we isolated and identified 56 strains of R. anatipestifer from the eastern regions of Hebei Province, China, and further determined their serotypes, antibiotic resistance, and pathogenicity. A total of 75 strains of causative bacteria were isolated from 70 sick geese with serositis. After Gram staining microscopy, PCR, and 16S rDNA sequence analysis, 56 isolates were identified as members of R. anatipestifer and 19 as Escherichia coli (E. coli). The results of serotyping showed that there were 4 serotypes prevalent in the isolate, including serotype 1 (37/56), serotype 2 (9/56), serotype 11 (8/56), and serotype 13 (2/56). The results of antibiotic susceptibility testing revealed that all 56 R. anatipestifer isolates showed varying degrees of multidrug resistance (MDR). A total of 10 antibiotic resistance genes (ARG) were determined in these isolates. Four isolates of different serotypes were selected for pathogenicity examination, and all were able to reproduce serositis-like symptoms in 15-day-old goslings, with neurological symptoms and a 100% mortality rate. Hemorrhagic congestion of the brain tissue, steatosis of the hepatocytes, and disorganization of some cardiac myofibers were observed in R. anatipestifer-infected geese. All these findings will contribute to our insights into the prevalence characteristics, antibiotic resistance profile, and pathogenicity of R. anatipestifer infection in geese in eastern Hebei Province and provide scientific guidance for the treatment and control of this disease.

Background: Bovine respiratory syncytial virus (BRSV) is a significant cause of bovine respiratory disease, resulting in significant losses to the cattle industry. For rapid detection of BRSV, a real-time recombinase-aided isothermal amplification assay (qRT-RAA) based on the F gene of BRSV was developed in this study. Results: The developed qRT-RAA assay showed good exponential amplification of the target fragment in 20 min at a constant temperature of 39 °C. And this assay displayed a high specificity for BRSV, without cross-reactions with Infectious Bovine Rhinotracheitis Virus (IBRV), Bovine Parainfluenza Virus Type 3 (BPIV3), Bovine Viral Diarrhea Virus (BVDV), and Bovine Coronavirus (BCoV). With the standard RNA of BRSV serving as a template, the limit of detection for qRT-RAA was 102 copies/μL. We examined ninety-seven clinical samples from cattle with respiratory disease using this method and determined a positive rate of 7.2% (7/97), consistent with results using the classical PCR method reported previously. Conclusions: A qRT-RAA assay for BRSV detection was established in this study. The method is specific and sensitive and can be completed within 20 min at 39 °C. These works demonstrate that the generated qRT-RAA assay is an effective diagnostic tool for rapidly detecting BRSV in resource-limited settings, which may be applied for the clinical detection of BRSV.

Elizabethkingia miricola is an emerging nosocomial pathogen responsible for meningitis, sepsis, urinary tract infection, pneumonia, and joint infection in humans. These pathogens were also reported to be causal agents for meningitis‐like disease in cultured frogs, which displayed high infectivity, mortality, and significant loss. In July 2023, 10 outbreaks of infectious meningitis‐like disease in bullfrogs occurred in Tangshan area. To determine the causal agent, 70 diseased frogs from 10 farms were collected for etiological identification. Gram‐negative bacilli were isolated from the brain and liver of sick bullfrogs and identified as members of E. miricola by biochemical characterization and 16S rRNA sequencing analysis. A total of 42 strains of E. miricola were isolated and further determined as the etiological agent by reproducing neurological symptoms and deaths in an artificial infection test. A representative isolate, HBTS‐1, was picked up for the pathogenicity test, and the data showed that this stain was highly pathogenic to bullfrogs with an LD₅₀ of 3.7 × 10⁵ CFU. Notably, the isolate also showed high pathogenicity to 5‐day‐old suckling mice, with an LD₅₀ of 3.1 × 10⁶ CFU, indicating its potential threat to mammals. Moreover, all the 42 E. miricola isolates showed resistance to multiple antibotics without an apparent inhibition zone observed in the test, making the choice of antimicrobial therapy challenging. These novel findings prioritized E. miricola as an important zoonotic agent, which may provide a reference for human medicine.

Bacterial pneumonia is a leading cause of mortality in fur-bearing animals, posing significant threat to fur production. To clarify the pathogenic agent of bacterial pneumonia in farmed foxes from eastern Hebei province, China, we performed bacterial isolation and identification from samples between 2020 and 2023. A total of 142 bacterial strains were isolated, of which 101 were identified as Escherichia coli (E. coli), indicating that E. coli is the major cause responsible for bacterial pneumonia in farmed foxes. Serotyping identification showed that a total of 8 serotypes were prevalent in the E. coli isolates, with O1, O8, O78 and O12 being the dominant ones. Five E. coli isolates were randomly picked for pathogenicity testing, and all of them were able to cause pneumonia symptoms in 6-week-old Kunming mice, accompanied by organ damage in lung. Eleven virulence genes were demonstrated present among the E. coli isolates. Antibiotic susceptibility tests showed that 78 of 101 E. coli strains exhibited multi-drug resistance (MDR), with the highest resistance rates against tetracyclines, and some strains showed resistance to carbapenems. Notably, no single antibiotic was effective against all strains. Twenty antibiotic resistance genes (ARGs) were detected among the isolates. Multilocus sequence typing (MLST) revealed 11 sequence types (STs) among 19 E. coli isolates, with ST-101 predominating (4/19). These findings enhance our understanding of the epidemiology, resistance traits, and pathogenicity of fox-derived pathogenic E. coli in Hebei.

Background: Salmonella has the ability to adapt to variable environments by modulating metabolism. The Tricarboxylic Acid Cycle (TCA), as a core metabolic process, is critical for the environmental adaptation and infection process of Salmonella. Fumarate reductase FrdA is an important enzyme in the TCA cycle, mainly catalyzing the conversion of fumarate to succinate. But the association between this enzyme and the pathogenicity of Salmonella has not yet been reported.Methods: To determine the role of fumarate reductase FrdA in Salmonella infection, a frdA-gene deletion strain of Salmonella enteritidis (S. enteritidis) was generated in this study, and the effect of frdA knockout on the biological properties and pathogenicity of S. enteritidis were further examined. Then, the immunoprotective effect of frdA-deficient strain was determined.Results: The results showed that frdA deletion did not affect the growth properties of S. enteritidis but caused a significant decreased survival under environmental stress, as well as a substantial decrease in its motility and biofilm formation ability. The ΔfrdA mutant displayed apparently reduced adhesion and invasion to Caco-2 cells and markedly impaired survival and replication in RAW264.7 cells. The animal infection test showed that the frdA gene deletion could lead to a significant decrease in virulence of S. enteritidis in mice, with a 64-fold increased LD₅₀ for mice, and ΔfrdA demonstrated significantly decreased colonization in mouse tissues and organs. The transcriptomics results showed that frdA deletion resulted in altered expression of 2163 genes in S. enteritidis, and downregulated expression of csgD and other virulence genes were confimed by qPCR. Moreover, immunization of mice with the frdA deletion strain provided promising immune protection for mice.Conclusion: Fumarate reductase FrdA is closely associated with pathogenicity of S. enteritidis and that is an attractive candidate target for vaccine design of Salmonella.