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Research Article | 09 Nov 2026

Fecal carriage of third-generation cephalosporin-resistant Escherichia coli harboring antimicrobial resistance and virulence-associated genes in healthy companion dogs in Thailand

Parinya Sroithongkham1,2, Chanita Noynoo3, Thanaphon Kaewprasert3, Phonpawee Somrat3, Atithep Phupasuk3, Phimonphorn Sianglam2, Pakpoom Navanukraw4, Patchara Phuektes1,2, and Suphattra Jittimanee1,2 Show more
VETERINARY WORLD | Article No. 7 | pg no. 5035-5050 | Vol. 19, Issue 11 | DOI: 10.14202/vetworld.2026.5035-5050
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ABSTRACT

                      
Background and Aim: Third-generation cephalosporin (3GC)-resistant Escherichia coli in companion animals represents an important One Health concern because apparently healthy dogs may carry antimicrobial-resistant bacteria with virulence-associated characteristics. This study aimed to determine the prevalence of fecal carriage of 3GC-resistant E. coli in clinically healthy companion dogs in Khon Kaen, Thailand, and to characterize their antimicrobial resistance (AMR) profiles, extended-spectrum β-lactamase (ESBL) production, blaCTX-M variants, phylogenetic groups, and extraintestinal virulence-associated genes.
Materials and Methods: A cross-sectional study was conducted from June to September 2025 using rectal swabs from 129 clinically healthy dogs attending five veterinary clinics using convenience sampling. 3GC-resistant isolates were identified using selective culture and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. ESBL production was assessed using combination disk testing, and antimicrobial susceptibility was determined using disk diffusion. Polymerase chain reaction and Sanger sequencing were used to characterize blaCTX-M genes. Phylogenetic grouping and virulence-associated gene screening were performed to identify molecular profiles consistent with extraintestinal pathogenic E. coli (ExPEC) and uropathogenic E. coli (UPEC).
Results: 3GC-resistant E. coli was detected in 31/129 dogs (24.0%; 95% confidence interval: 17.4%–32.2%), yielding 32 isolates, including two phenotypically distinct isolates from one dog. Among these, 27/32 (84.4%) exhibited an ESBL-producing phenotype, and 22/27 (81.5%) ESBL-producing isolates carried blaCTX-M genes. The identified variants included blaCTX-M-55 (7/22), blaCTX-M-15 (6/22), blaCTX-M-27 (6/22), and blaCTX-M-14 (3/22). Multidrug resistance (MDR) was observed in 25/32 isolates (78.1%). Phylogroup B2 predominated (15/32, 46.9%) and exhibited substantial virulence-gene carriage. One isolate (3.1%) met molecular criteria for UPEC only, five (15.6%) for ExPEC only, and seven (21.9%) for both pathotypes.
Conclusion: Clinically healthy companion dogs carried 3GC-resistant E. coli exhibiting MDR and virulence-associated molecular characteristics. These findings highlight the importance of companion animal AMR surveillance and responsible antimicrobial use within the One Health framework. However, the reported prevalence is limited to the sampled dogs and molecular pathotype classification does not independently establish clinical pathogenicity or zoonotic transmission.
                      
Keywords: antimicrobial resistance, companion dogs, Escherichia coli, extended-spectrum β-lactamase, extraintestinal pathogenic Escherichia coli, multidrug resistance, third-generation cephalosporins, virulence-associated genes.