Occurrence and characterization of Salmonella isolates from commercial eggs in Phayao Province, Thailand

Vet World Vol.18 March-2025 Article - 17

Research Article

Veterinary World, 18(3): 705-714

https://doi.org/10.14202/vetworld.2025.705-714

Watsawan Prapasawat¹, Anchalee Rawangkan^2,3, Chittakun Suwancharoen^2,3, Atchariya Yosboonruang^2,3, Anong Kiddee^2,3, Watchara Laenoi⁴, Sirikarn Wiriyasirivaj¹, Orasa Suthienkul⁵, and Achiraya Siriphap^2,3

1. Department of Clinic, Faculty of Veterinary Medicine, Mahanakorn University of Technology, Bangkok, 10530, Thailand.
2. Division of Microbiology and Parasitology, School of Medical Sciences, University of Phayao, Phayao, 56000, Thailand.
3. Unit of Excellence on Research and Application of Natural Products for Health and Well-Being, University of Phayao, Phayao, 56000, Thailand.
4. Division of Animal Science, School of Agriculture and Natural Resources, University of Phayao, Phayao, 56000, Thailand.
5. Department of Microbiology, Faculty of Public Health, Mahidol University, Bangkok, 10400, Thailand.

Background and Aim: Salmonella contamination in eggs poses a significant public health risk, particularly in alternative egg production systems where contamination and antimicrobial resistance remain underexplored. This study aimed to determine the occurrence of Salmonella contamination in three different egg production systems in Phayao, Thailand, and analyze serovar diversity, antimicrobial resistance, virulence genes, and genetic profiles.

Materials and Methods: A total of 750 eggs were sampled from cage, free-range, and organic egg production systems, purchased from supermarkets in Phayao Province. Eggshells and contents were separately analyzed using conventional microbiological methods to isolate Salmonella. Phenotypic identification, serotyping, and antimicrobial susceptibility testing were performed. Genotypic characterization, including virulence and antimicrobial resistance gene detection, was conducted using polymerase chain reaction. Multilocus sequence typing (MLST) was employed to determine genetic diversity.

Results: Salmonella contamination was detected in three eggshell samples (0.4%), with one positive sample from each production system. The identified serovars were Salmonella Mbandaka (cage eggs), Salmonella Corvallis (free-range eggs), and Salmonella Cerro (organic eggs). Antimicrobial resistance was observed in only one isolate, S. Mbandaka, which exhibited resistance to sulfamethoxazole/trimethoprim and carried the sul1 and sul2 genes. All Salmonella isolates harbored virulence genes (invA, sopB, and stn). MLST analysis identified three distinct sequence types (ST413, ST1541, and ST1593) corresponding to the detected serovars.

Conclusion: This study demonstrates a low occurrence of Salmonella contamination in eggshells across different production systems, with no contamination detected in egg contents. The presence of distinct serovars and genetic types suggests varying contamination sources. Although antimicrobial resistance was minimal, the presence of virulence genes in all isolates highlights the potential risk of infection. Continuous monitoring and improved biosecurity measures in egg production and distribution are recommended to enhance food safety and public health.

Keywords: antimicrobial resistance, eggs, food safety, multilocus sequence typing, Salmonella, virulence genes.

How to cite this article: Prapasawat W, Rawangkan A, Suwancharoen C, Yosboonruang A, Kiddee A, Laenoi W, Wiriyasirivaj S, Suthienkul O, and Siriphap A (2025) Occurrence and characterization of Salmonella isolates from commercial eggs in Phayao Province, Thailand, Veterinary World, 18(3): 705-714.

Received: 2024-10-17 Accepted: 2025-02-25 Published online: 2025-03-23

Corresponding author: Achiraya Siriphap E-mail: achiraya.si@up.ac.th

DOI: 10.14202/vetworld.2025.705-714

Copyright: Prapasawat, 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.