Antimicrobial resistance and molecular genetic characteristics of monophasic Salmonella Typhimurium carried by healthy population in Yulin, Guangxi Zhuang Autonomous Region

  Objective  To understand the drug resistance and phylogenetic characteristics of monophasic Salmonella Typhimurium isolated from healthy population in Yulin, Guangxi Zhuang autonomous region.

  Methods  A total of 147 strains of monophasic S. Typhimurium were isolated from healthy people engaged in food process from 2021 to 2022 for serotyping and drug susceptibility test to 16 antimicrobial agents using micro-broth dilution method. Molecular subtyping and cluster analysis were performed by pulse-field gel electrophoresis (PFGE). Whole genome sequencing and multi locus sequence typing were performed to explore the genetic characteristics of the strains.

  Results  The drug resistance of monophasic S. Typhimurium was common. The drug resistant strains accounted for 98.64%. The resistance of monophasic S. Typhimurium to streptomycin was highest (96.60%), followed by ampicillin (91.16%) and tetracycline (91.16%). The multi-drug resistant rate was 85.71%, and the main drug resistant profile was resistant to ampicillin, streptomycin and tetracycline simultaneously. A total of 132 PFGE patterns were identified in 147 strains, and some clusters were observed, but the strains in the clusters showed high genetic diversities in genomes. The phylogenetic tree based on core genome showed three potential clonal clusters in 147 strains. Multi locus sequence typing showed that ST34 was the predominant type, accounting for 96.60% of all strains.

  Conclusion  The drug resistance of monophasic S. Typhimurium carried by healthy population in Yulin was serious. The strains had high genetic diversity, indicating the potential for outbreaks. The study results suggest that health monitoring and risk factor identification should be further strengthened to reduce the spread of emerging serotype of Salmonella with high antimicrobial resistance.