Antimicrobial Resistance and Molecular Characterization of Salmonella Rissen Isolated in China During 2008–2019

Background: This study aimed to provide epidemiological features of Salmonella enterica serovar Rissen, determine antimicrobial susceptibility, virulence gene profiles, and describe the potential association of S . Rissen from different sources in China. Methods: During 2008– 2019, a total of non-repetitive 228 S . Rissen isolates were collected from human, animals and environment in China. The antimicrobial susceptibility test, screening of antimicrobial and virulence genes by PCR, and pulsed-field gel electrophoresis (PFGE) were performed. Results: Among the 154 isolates from human, the majority of the cases (80.5%) occurred in summer, and S . Rissen was mainly detected in people aged 21– 40 (37.7%) and 41– 60 (28.6%) years old, and 74 non-human source S . Rissen strains were identified, with pork being the most common source. About 93.4% isolates were resistant to at least one of the 12 tested antimicrobial agents, and high frequencies of resistance were observed for tetracyclines (91.2%), trimethoprim-sulfamethoxazole (74.1%) and ampicillin (67.5%). A total of 171 (75%) isolates were resistant to at least three categories of antimicrobials, and the most common resistance profile was Tetracycline(s)-β-Lactams-Sulfonamides. The resistance rates to chloramphenicol, quinolones and sulfafurazole were significantly higher in strains isolated from human compared to non-human source strains. Among these isolates, the β-Lactams resistance was mainly associated with gene bla TEM (54.7%), sulfonamide resistance with sul2 (45.7%) and sul3 (54.3%), tetracycline resistance with tetA (81.3%). All the isolates harbored virulence genes hilA, sopB, sciN, stn and ssrB , and most of them harbored ssaQ (98.7%), mgtC (98.7%) and invA (98.2%). The majority (91.7%) of S . Rissen isolates showed high similarity (> 80%) with each other in PFGE patterns and came from human, animals and environment. Conclusion: The high frequencies of multidrug resistance and probable clonal dissemination in this serovar call for the necessity of systematic surveillance on S . Rissen in China.