Vet World   Vol.18   June-2025  Article - 14 

Molecular epidemiology and antimicrobial resistance of Salmonella at the human–macaque–environment interface in Thailand: A One Health surveillance study

Background and Aim: The close interaction between humans and free-ranging macaques in urbanized environments raises concerns about the potential transmission of antimicrobial-resistant zoonotic pathogens. This study applied a One Health approach to estimate the prevalence, serovar distribution, antimicrobial resistance (AMR), and genetic diversity of Salmonella spp. in long-tailed macaques (Macaca fascicularis) and environmental sources in Chonburi, Thailand.

Materials and Methods: A total of 313 samples – including 224 rectal swabs from macaques and 89 environmental samples (pooled macaque feces, stray dog feces, soil, feed, and drain water) – were collected from Si Racha and Sattahip districts between April and July 2023. Salmonella isolation was conducted using conventional culture methods, followed by confirmation through serotyping and polymerase chain reaction targeting the invA gene. Antimicrobial susceptibility testing was performed against 14 agents using broth microdilution. Multi-locus sequence typing and 16S rRNA gene sequencing were conducted to assess phylogenetic diversity.

Results: The overall prevalence of Salmonella was 2.88%, with all positive samples detected in the Si Racha district. Environmental samples had a significantly higher prevalence (8.89%) than macaque rectal swabs (0.45%; odds ratio = 22; 95% confidence interval: 2.71–178.84; p = 0.0002). Six distinct serovars were identified, with Salmonella Corvallis predominating in macaque feces. Among the nine isolates, 77.78% exhibited resistance, primarily to tetracycline and ampicillin. Notably, 85.71% of AMR strains from environmental samples were multidrug-resistant (MDR), showing resistance to ≥6 antimicrobials. Phylogenetic analysis revealed genetic heterogeneity, with no clear clustering by source or serovar.

Conclusion: This study underscores the circulation of MDR Salmonella within macaques and their surrounding environments, implicating environmental reservoirs in potential zoonotic and reverse zoonotic transmission. The findings advocate for public awareness initiatives, environmental hygiene improvements, and integrative One Health strategies to mitigate AMR dissemination at the human–animal–ecosystem interface.

Keywords: antimicrobial resistance, environmental reservoirs, macaques, molecular typing, One Health, Salmonella, Thailand, zoonosis.

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How to cite this article: Pornsukarom S, Tongthainan D, Phromwat P, Wannaratana S, Nakbubpa K, and Muangsri S (2025) Molecular epidemiology and antimicrobial resistance of Salmonella at the human–macaque–environment interface in Thailand: A One Health surveillance study, Veterinary World, 18(6): 1549-1560.

Received: 25-02-2025   Accepted: 15-05-2025   Published online: 15-06-2025

Corresponding author: Suchawan Pornsukarom    E-mail: suchawan_po@rmutto.ac.th

DOI: 10.14202/vetworld.2025.1549-1560

Copyright: Pornsukarom, et al. This article is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http:// creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.