Dynamic Serotype Distribution and Antimicrobial Resistance of Salmonella Isolates from 2019 to 2023 in Guizhou, China.

Introduction: Salmonella, a leading cause of human infectious diarrhea diseases, foodborne illness, and zoonotic infections, poses a significant health burden.

Methods: A retrospective screening was performed to elucidate the serotype distribution and antimicrobial resistance of 933 human Salmonella isolates from nine cities (prefectures) in Guizhou province of southwestern China between 2019 and 2023 through slide agglutination and antimicrobial resistance testing.

Results: Fifty-four different serotypes were identified in this study, with S. Typhimurium (44.4%) and S. Enteritidis (20.7%) being the predominant serotypes, followed by S. London (3.1%), S. Derby (2.8%), and S. Rissen (2.0%). A total of 39 serotypes were reported for the first time in Guizhou province, and 121 isolates (13.0%) could not be classified. The diversity of Salmonella serotypes in Guizhou has increased from 8 in 2019 to 39 in 2023. In addition, the detection rate of S. Enteritidis showed a decreasing trend over time, while the detection rate of S. Typhimurium demonstrated an annual increase since 2020. For 933 isolates, a significant majority (94.0%) exhibited resistance to at least one class of antimicrobial agents. The highest resistance observed was to ampicillin (86.4%), followed by resistance to tetracycline (76.3%) and streptomycin (72.8%). Notably, we discovered that the resistance rate to colistin was 4.7%, with 93.2% of these isolates being S. Enteritidis. Meanwhile, 78.5% of isolates were demonstrated multidrug resistance (MDR), with the MDR rates for S. Rissen and S. Typhimurium exceeding 90%. Additionally, 5.7% of Salmonella isolates were extensively drug-resistant (XDR), with S. Typhimurium and S. Enteritidis exhibiting XDR rates of 5.1% and 4.1%, respectively. The rate of MDR and XDR in Salmonella peaked in 2019 and then gradually declined from 2020 to 2022, rising again in 2023.

Conclusion: Our research revealed an increasing diversity in Salmonella serotypes within Guizhou province, alongside significant challenges posed by MDR and a rising XDR rate. Therefore, it is essential to continuously improve the surveillance of Salmonella, keep track of changes in serotype distribution and dynamic shifts, and strengthen the persistent monitoring of antimicrobial agents.