To explore the risk of antimicrobial resistant (AMR) non-typhoidal Salmonella during asymptomatic infection passage between pet dogs and human caregivers in Khon Kaen, Thailand, one hundred forty paired fecal samples (n = 280) were obtained from companion dogs and their human caregivers, interviewed from 140 households during 2019–2020. The purified Salmonella isolates were serotype-identified and tested for antimicrobial resistance against ampicillin, ciprofloxacin, chloramphenicol, nalidixic acid, streptomycin, sulfamethoxazole–trimethoprim, and tetracycline. The homologous Salmonella isolate pairs (suggesting Salmonella infections may have been due to passage between each one of the pair, or derived from the same source) were subsequently characterized by serotype screening, pulsed field gel electrophoresis (PFGE), and Synchrotron Fourier transform infrared spectroscopy (SR-FTIR). The Salmonella prevalence observed in dogs, 12.86% (18/140), was not significantly different from that observed in humans, 17.86% (25/140) using McNemar’s test. The AMR patterns (the patterns among the isolates of pet dogs and caregivers) and the serotypes (thirteen serotypes with 18 isolates from pet dogs plus thirteen serotypes with 25 isolates from humans) between pet dogs and humans were not significantly different using Pearson’s chi-squared test. The homologous Salmonella isolates from the Salmonella-present households was 5.13% (2/39). This study demonstrated that the hypothesis that there is a high risk of Salmonella infection passage between dogs and humans with close contact in Khon Kaen is doubtful. Only 5.13% of homologous Salmonella isolates from Salmonella-present households were found in Khon Kaen, Thailand, although the prevalence of Salmonella-positive samples, serotypes, and antimicrobial resistance patterns were quite similar among the two populations.

To evaluate the containment of antimicrobial-resistant (AMR) Salmonella contaminations of a HACCP slaughterhouse (HACCP SH) and a non-HACCP slaughterhouse (non-HACCPSH), 360 paired pig rectal (representing the farm pig status) and carcass samples (representing the contamination) were collected equally from the two slaughterhouses that serviced 6 and 12 farms, respectively, in Northeast Thailand (n = 720). The purified Salmonella isolates were serotype identified, antimicrobial susceptibility tested, and pulsed-field gel electrophoresis (PFGE) assessed. Four evaluations of two slaughterhouses were examined: (1) the means of slaughtering contamination rates (SCR) (to evaluate the contamination level by averaged farm SCRs): the HACCP SH decreased contamination (SCR: −48.89% ± 8.80%, n = 6), whereas the non-HACCP SH increased (SCR: 14.31% ± 9.35%, n = 12). (2) The serotype diversity: the HACCP SH decreased the diversity from the rectal group (110 isolates, 9 serotypes) to carcass group (23 isolates, 3 serotypes), whereas there was no decrease in the non-HACCP SH (rectal group (66 isolates, 14 serotypes) and carcass group (31 isolates, 10 serotypes)). (3) The AMR patterns: the HACCP SH decreased from rectal group (96 isolates, 7 patterns) to carcass group (22 isolates, 1 pattern), whereas there was no decrease from the non-HACCP SH rectal group (22 isolates, 7 patterns) to carcass group (48 isolates, 8 patterns). (4) The estimated indirect contamination rate (by serotype screening and PFGE confirmation): the HACCP SH was 60.87% (14/23), whereas the non-HACCP SH was 98.48% (65/66). This study indicates that both the slaughterhouses keep a high level of indirect contamination; the HACCP SH decreases Salmonella contaminations and reduces the AMR patterns, the non-HACCP SH increases contaminations.

Background: Mobile antimicrobial resistance genes (ARGs) on plasmids or other elements enable Salmonella Typhimurium to spread resistance across hosts and environments. The emergence of multi-drug resistance (MDR) Salmonella Typhimurium has raised global concern, yet little is reported about these mobile elements from the Thailand pork supply chain, where this risk of transfer to humans remains largely uncharacterized. Methods: Between March 2023 and February 2024, 25 S. Typhimurium isolates were collected from pig carcasses in slaughterhouses and pork swabs from retail markets in northeastern Thailand. Nine representative isolates, sampled across three seasons, were subjected to Illumina whole-genome sequencing. Assemblies were analyzed for sequence types, phylogenetic relationships, antimicrobial resistance (AMR) determinants, plasmid replicons and mobilization features, functional annotation based on COG (Clusters of Orthologous Groups of proteins) classification, and comparative genomics against a reference strain. Results: Genome assemblies ranged from 4.76 to 5.00 Mb with consistent GC (guanine-cytosine) content (52.0–52.2%). Phylogenetic analysis revealed three sequence types: ST34 (77.8%), ST19, and ST1543. ST34 isolates displayed the broadest AMR gene repertoires, carrying tetracycline (tetA/tetB), sulfonamide (sul1/sul2/sul3), aminoglycoside (aadA, aph(6)-Id, aph(3″)-Ib), phenicol (floR, catA1), and β-lactam (bla_TEM-1B) genes, whereas non-ST34 isolates harbored fewer determinants. ARGs frequently co-localized with IncQ1 and Col-type plasmid replicons, MOB_H/MobA relaxases (enzymes that initiate plasmid transfer), and conjugation modules (type IV secretion and coupling proteins), often alongside virulence loci and metal resistance operons. Functional annotation showed highly conserved metabolic and housekeeping functions, while comparative genomics confirmed >90% core genome conservation, with variability concentrated in genomic islands encoding hypothetical proteins. These genomic patterns were inferred from a limited WGS dataset (nine isolates) and should therefore be considered exploratory and require confirmation in larger collections. Conclusions: Multi-drug resistant ST34 Salmonella Typhimurium predominated in the northeastern Thailand pork supply chain, with diverse resistance genes carried on IncQ1/Col-type plasmids linked to MOB_H relaxases and conjugation modules. The stability of these mobilizable elements underscores their role in sustaining MDR traits and highlights the risk of foodborne AMR transmission, reinforcing the need for continuous genomic surveillance under a One Health framework.

Salmonella remains a critical foodborne pathogen of public health importance and a predominant contributor to contamination throughout the pork production system. However, in northeastern Thailand, detailed characterization of seasonal variation and stage-specific occurrence, including pre-slaughter fecal samples, post-slaughter carcasses, and retail pork, has been largely lacking. Clarifying the influence of seasonal conditions on Salmonella prevalence and antimicrobial resistance across these production points is essential for robust risk assessment within the pork supply chain. A total of 897 samples were collected from slaughterhouses (carcasses, feces) and markets (pork) in northeastern Thailand during the summer, rainy, and winter seasons from 2023 to 2024. Salmonella isolation, serotyping, antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE), and phylogenetic analysis were performed to assess prevalence, serotype distribution, AMR, and genetic relatedness. The associations between prevalence or AMR and seasonal factors were evaluated using relative risk (RR), chi-square, and logistic regression tests. Salmonella prevalence varied markedly across matrices and seasons. Retail pork showed the highest contamination (summer: 75.4%, rainy: 75.3%, winter: 54.7%), followed by feces (50.5%, 34.0%, and 29.0%, respectively), whereas carcass samples had the lowest prevalence (11.3%, 13.0%, and 4.0%). Seasonal effects were significant for fecal (χ² = 11.4, P = 0.003) and pork samples (χ² = 7.7, P = 0.021). Relative risk (RR), using winter as reference, reached 1.7 for fecal samples and 1.4 for pork during summer. Serotype composition exhibited pronounced seasonal shifts, with S . Rissen increasing sharply and becoming dominant in winter; logistic regression showed significantly lower odds of S . Rissen isolation in summer (OR = 0.25, P < 0.01) and the rainy season (OR = 0.47, P < 0.01) compared with winter. Multivariable models indicated that the rainy season was strongly associated with antimicrobial resistance (OR = 11.9 vs winter, P = 0.002). S . Rissen remained the primary contributor to MDR across matrices, while S . Bovismorbificans and other serotype s showed significantly reduced resistance (OR = 0.2, P < 0.05). PFGE analyses revealed high polymorphism in S . Weltevreden (55%–100% similarity) and S . Rissen (50%–100%), with no clustering by matrix or season, indicating cross-environmental dissemination of similar clones. Phylogenetic analysis identified two major S . Rissen lineages but a highly conserved MDR gene backbone, including β-lactamases (blaTEM-1, blaCTX-M-55), aminoglycoside resistance genes (aadA, aac(6′)-Iy), phenicol resistance genes (cmlA6, floR), sulfonamide and trimethoprim resistance genes, and PMQR determinants (qnrB10, qnrS1). Salmonella contamination and antimicrobial resistance in the pork production chain are strongly shaped by seasonal pressures and downstream amplification during distribution. Summer and the rainy season present the highest risk for both contamination and multidrug resistance, while winter shows marked serotype convergence, dominated by S . Rissen. Retail pork exhibited the most complex MDR profiles, indicating an accumulation of resistance along the supply chain. PFGE and phylogenetic analyses revealed that closely related clones circulate across slaughterhouses and markets, supporting persistent transmission routes. These findings highlight the need for strengthened seasonal risk management and integrated genomic surveillance to interrupt the spread of high-risk MDR serotypes and reduce consumer exposure. IMPORTANCE: Understanding when and how Salmonella spreads along the pork production chain is essential for reducing human exposure to foodborne pathogens and multidrug-resistant (MDR) strains. This study identifies strong seasonal pressures and downstream amplification during distribution as key drivers of Salmonella contamination and antimicrobial resistance. The marked winter dominance of MDR S . Rissen and the accumulation of complex resistance profiles in retail pork highlight predictable high-risk periods and critical control points where interventions can be most effective. Furthermore, the discovery that closely related clones circulate between slaughterhouses and markets underscores persistent transmission routes that conventional hygiene measures may fail to interrupt. By integrating epidemiological, phenotypic, and genomic evidence, this work provides actionable insights for designing season-specific monitoring programs and implementing genomic surveillance to limit the spread of MDR Salmonella in the food supply.

Background and Aim: Salmonella is a major foodborne zoonotic pathogen that threatens public health and poultry production worldwide. Although its prevalence and antimicrobial resistance (AMR) in Thai poultry have been widely reported, continuous comparative surveillance across slaughterhouses and retail markets with seasonal stratification remains limited, particularly in Northeast Thailand. This study aimed to systematically compare the prevalence, serotype distribution, AMR profiles, and genetic relatedness of Salmonella isolates recovered from chicken slaughterhouses and retail markets, with emphasis on seasonal and supply chain variations. Materials and Methods: A total of 689 swab samples were collected from two slaughterhouses and two retail markets in Khon Kaen Province, Thailand, across three seasons (summer, rainy, and winter) from March 2023 to February 2024. Isolation and identification of Salmonella were performed according to ISO 6579-1:2017. Serotyping was conducted using the White–Kauffmann–Le Minor scheme. Antimicrobial susceptibility testing was performed against 14 antibiotics using the disk diffusion method following Clinical and Laboratory Standards Institute guidelines. Genetic relatedness of selected isolates was assessed using pulsed-field gel electrophoresis. Statistical analyses included chi-square tests, relative risk estimation, and multivariable logistic regression. Results: The overall prevalence of Salmonella was 32.37% (223/689), with significantly higher contamination in retail markets than slaughterhouses. Prevalence peaked during the rainy season (45.29%), whereas multidrug resistance was highest in winter, particularly in slaughterhouse isolates. The predominant serotypes were Salmonella Agona (15.25%) and Salmonella Saintpaul (14.79%). High resistance rates were observed to streptomycin (43.05%), ampicillin (34.53%), and nalidixic acid (30.49%). Multidrug resistance was detected in 32.43% of isolates. Logistic regression analysis identified retail markets and rainy and winter seasons as independent risk factors for contamination. Pulsed-field gel electrophoresis demonstrated clonal relatedness among isolates within similar locations and seasons, with evidence of cross-contamination along the supply chain. Conclusion: This study provides a comprehensive, year-round comparative assessment of Salmonella contamination and AMR in slaughterhouses and retail markets in Northeast Thailand. The distinct seasonal dissociation between peak prevalence and peak multidrug resistance highlights the need for season-specific and site-targeted surveillance and intervention strategies within the poultry supply chain. Keywords: antimicrobial resistance, chicken, food safety, genetic relatedness, prevalence, poultry supply chain, seasonal variation, Salmonella.

Hepatitis E, caused by the hepatitis E virus (HEV), is a zoonotic disease that extends beyond hepatocellular necrosis to replicate in multiple organs. While most infections are self-limiting, HEV infection during pregnancy is associated with severe outcomes, including acute liver failure, preterm delivery, and miscarriage, with the mechanisms underlying this high pathogenicity remaining poorly understood. This study established a pregnant tree shrew model with a late-stage HEV infection and a cellular model using zoonotic HEV genotypes GT3 and GT4 to investigate the effects of estrogen on HEV replication. Results showed that negative-strand RNA detection revealed replicative intermediates in feces and tissues during the acute phase, with peak viral loads occurring within one week and the highest titers in bile. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels rose at 3 days post-inoculation (DPI), peaking at 7 DPI. Elevated estrogen levels post-miscarriage correlated with increased viral loads, a trend mirrored in cell culture models showing linear relationships between estrogen and viral replication. Histopathology demonstrated viral hepatitis lesions in liver tissues and abnormalities in the uterus, ovaries, and brain, including hydropic degeneration, neuronal disruption, and granulosa cell necrosis. This study developed a pregnant tree shrew model for HEV infection, providing a robust tool for exploring pathogenic mechanisms during pregnancy and genotype-specific differences in zoonotic HEV pathogenicity. These findings offer new insights into the role of estrogen in HEV replication and its contribution to adverse pregnancy outcomes.