Abstract:[Background] Riemerella anatipestifer (RA) is the pathogen that causes infectious serositis in a variety of domesticated and wild birds such as ducklings, geese, and turkeys. With wide distribution all over the world, it endangers the development of poultry industry and causes serious economic losses. [Objective] To learn the epidemic status and biological characteristics of RA in China and guide the prevention and control of RA-caused disease. [Methods] PCR, biochemical tests, and serotyping were carried out for the suspected RA strains isolated from Shandong province, Hebei province, Guangdong province, and Shanxi province from 2020 to 2021. The drug resistance of the strains was evaluated by drug sensitivity test, and the pathogenicity was analyzed based on median lethal dose. [Results] A total of 78 RA strains were identified, including 4 strains of serotype 1, 21 strains of serotype 2, 11 strains of serotype 10, 3 strains of serotype 6, and 17 strains of serotype 7, 1 strain with cross agglutination, and 21 strains not serotyped. The 78 strains had the strong drug resistance to polymyxin B, fosfomycin, and clindamycin and were sensitive to cefradine, doxycycline, furazolidone, and florfenicol. In addition, all the 78 strains had multiple drug resistance, among which 77 strains had resistance to more than 5 antibiotics. The animal test results showed that the RA strains generally had strong pathogenicity, which varied among different strains of the same region and among strains of different regions. The LD 50 of 14 RA strains ranged from 104 to 107 CFU. [Conclusion] RA has demonstrated strong pathogenicity and drug resistance in China. The results of this study provide a basis for the prevention and control, clinical medication, and subsequent research on the pathogenic mechanism of RA.
