Epidemiological investigation and ß-lactam antibiotic resistance of Riemerella anatipestifer isolates with waterfowl origination in Anhui Province, China.

Riemerella anatipestifer (R. anatipestifer) is a highly pathogenic and complex serotypes waterfowl pathogen with inherent resistance to multiple antibiotics. This study was aimed to investigate the antibiotic resistance characteristics and genomic features of R. anatipestifer isolates in Anhui Province, China in 2023. A total of 287 cases were analysed from duck farms and goose farms, and the R. anatipestifer isolates were subjected to drug resistance tests for 30 antimicrobials. Whole genome sequencing (WGS) and bioinformatics analysis were performed on the bacterial genomes, targeting the ß-lactam resistance genes. The results showed that a total of 74 isolates of R. anatipestifer were isolated from 287 cases, with a prevalence of 25.8%. The antimicrobial susceptibility testing (AST) revealed that all the 74 isolates were resistant to multiple drugs, ranging from 13 to 26 kinds of drugs. Notably, these isolates showed significant resistance to aminoglycosides and macrolides, which are also commonly used in clinical practices. Data revealed the presence of several ß-lactamase-related genes among the isolates, including a novel blaRASA-1 variant (16.2%), the class A extended-spectrum ß-lactamase blaRAA-1 (12.2%), and a blaOXA-209 variant (98.6%). Functional analysis of the variants blaRASA-1 and blaOXA-209 showed that the blaRASA-1 variant exhibited activity against various ß-lactam antibiotics while their occurrence in R. anatipestifer were not common. The blaOXA-209 variant, on the other hand, did not perform any ß-lactam antibiotic resistance. Furthermore, we observed that blaRAA-1 could undergo horizontal transmission among different bacteria via the insertion sequence IS982. In conclusion, this study delves into the high prevalence of R. anatipestifer infection in waterfowl in Anhui, China. The isolated strains exhibit severe drug resistance issues, closely associated with the prevalence of antibiotic resistance genes (ARG). Additionally, our research investigates the ß-lactam antibiotic resistance mechanism in R. anatipestifer.

Evaluation of histopathological changes, viral load and immune function of domestic geese infected with Newcastle disease virus.

Outbreaks of Newcastle disease in flocks of geese with high morbidity and mortality in southern and eastern China have been reported frequently since the late 1990s, which broke the traditional view that geese are considered to be the natural reservoir of Newcastle disease virus (NDV) but show few or no clinical signs after infection. In this present study, geese were infected intranasally with a local strain of NDV. Clinical disease and gross pathology were observed. Serum and immune organs were collected from geese sequentially euthanized or after disease-associated death. We studied the histopathology of immune organs by haematoxylin and eosin staining and NDV fusion protein was detected in tissues by immunohistochemistry. At the same time, the SYBR Green I real-time polymerase chain reaction assay was used to detect the viral load from the collected samples. Serum samples were tested for NDV-specific antibodies and avian influenza virus (AIV)-specific antibodies by haemagglutination inhibition (HI) test. The results showed that severe lesions and numerous positive reactions of NDV antigen were detected in the immune organs. High viral loads developed in immune organs of infected geese, correlating with the severity of clinical signs and lesions in the tissues. Furthermore, the infected geese developed low HI antibody titres to both AIV and NDV. The present study showed that the replication and dissemination of the NDV isolate was widespread in immune organs of geese. The study revealed that waterfowl may not only be a natural reservoir of NDV but also become susceptible to disease and may play a major role in the epidemiology of Newcastle disease.