Vet World   Vol.19   February-2026  Article - 19 

Molecular characterization of virulence and multidrug resistance in Escherichia coli isolated from houseflies (Musca domestica) at food markets in Northern Thailand

Background and Aim: Houseflies (Musca domestica) are recognized mechanical vectors of foodborne pathogens and antimicrobial-resistant bacteria, particularly in environments with intensive food-handling. Their role in disseminating virulent and multidrug-resistant (MDR) Escherichia coli at the food–environment–human interface remains underexplored in Northern Thailand. This study aimed to determine the prevalence, phylogenetic distribution, virulence gene carriage, antimicrobial resistance profiles, and resistance determinants of E. coli isolated from houseflies collected at food markets in Phayao Province. 

Materials and Methods: A cross-sectional surveillance study was conducted between June and November 2023 in Muang District, Phayao Province. A total of 350 houseflies were collected from meat, vegetable, and cooked-food markets using sticky traps. E. coli isolates were identified by culture and polymerase chain reaction (PCR) targeting the uidA gene. Phylogenetic grouping was performed using chuA, yjaA, and TSPE4.C2. Virulence genes associated with diarrheagenic E. coli were detected by PCR. Antimicrobial susceptibility testing was conducted using the disc diffusion method against 12 antibiotics representing eight antimicrobial classes. Multidrug resistance was defined as resistance to three or more antimicrobial classes. Resistance-associated genes were screened by PCR. Associations were analyzed using the chi-square test. 

Results: Overall, 106 E. coli isolates (30.3%) were recovered, with the highest prevalence in meat markets (39.5%) (p < 0.0001). Phylogroup A predominated (49.1%), followed by D (19.8%), B1 (18.9%), and B2 (12.3%). Virulence genes were detected in 69.8% of isolates, with bfpA being the most prevalent (26.4%). Universal resistance to penicillin G and erythromycin was observed, while high resistance rates were noted for ampicillin (66.0%) and tetracycline (35.8%). MDR was identified in 46.2% of isolates and was significantly more common in meat markets (p = 0.0225). The highest MDR prevalence occurred in phylogroup D (57.1%). The most frequently detected resistance genes were blaSHV, ereA, and tetA. 

Conclusion: Houseflies from food markets in Northern Thailand harbor virulent and MDR E. coli, highlighting their role as environmental sentinels and potential disseminators of antimicrobial resistance. These findings underscore the need for improved market hygiene and incorporation of insect vectors into One Health–based antimicrobial resistance surveillance strategies. 

Keywords: antimicrobial resistance, Escherichia coli, food markets, houseflies, multidrug resistance, Northern Thailand, One Health, virulence genes.

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How to cite this article: Khoothiam K, Upakut S, Siriphap A, Japa O, Thepmalee C, Suwannasom N. Molecular characterization of virulence and multidrug resistance in Escherichia coli isolated from houseflies (Musca domestica) at food markets in Northern Thailand. Vet. World. 2026;19(2):714-724.

Received: 04-11-2025   Accepted: 13-01-2026   Published online: 26-02-2026

Corresponding author: Krissana Khoothiam    E-mail: krissana.kh@up.ac.th

DOI: 10.14202/vetworld.2026.714-724

Copyright: Khoothiam, 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.