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This study aimed to investigate the potential mechanisms associated with the persistence of chloramphenicol (CHP) resistance in Escherichia coli and Salmonella enterica isolated from pigs, pork, and humans in Thailand. The CHP-resistant E . coli (n = 106) and Salmonella (n = 57) isolates were tested for their CHP susceptibility in the presence and absence of phenylalanine arginine β-naphthylamide (PAβN). The potential co-selection of CHP resistance was investigated through conjugation experiments. Whole genome sequencing (WGS) was performed to analyze the E . coli (E329, E333, and E290) and Salmonella (SA448, SA461, and SA515) isolates with high CHP MIC (32–256 μg/mL) and predominant plasmid replicon types. The presence of PAβN significantly reduced the CHP MICs (≥4-fold) in most E . coli (67.9%) and Salmonella (64.9%). Ampicillin, tetracycline, and streptomycin co-selected for CHP-resistant Salmonella and E . coli -transconjugants carrying cmlA . IncF plasmids were mostly detected in cmlA carrying Salmonella (IncFIIAs) and E . coli (IncFIB and IncF) transconjugants. The WGS analysis revealed that class1 integrons with cmlA1 gene cassette flanked by IS 26 and Tn As1 were located on IncX1 plasmid, IncFIA(HI1)/HI1B plasmids and IncFII/FIB plasmids. IncFIA(HI1)/HI1B/Q1in SA448 contained catA flanked by IS 1B and Tn As3 . In conclusion, cross resistance through proton motive force-dependent mechanisms and co-selection by other antimicrobial agents involved the persistence of CHP-resistance in E . coli in this collection. Dissemination of CHP-resistance genes was potentially facilitated by mobilization via mobile genetic elements.

This study aimed to determine the epidemiology and association of antimicrobial resistance (AMR) among Escherichia coli and Salmonella in Thailand. The E. coli (n = 1047) and Salmonella (n = 816) isolates from pigs, pork and humans were screened for 18 replicons including HI1, HI2, I1-γ, X, L/M, N, FIA, FIB, W, Y, P, FIC, A/C, T, FIIAs, F, K and B/O using polymerase chain reaction-based replicon typing. The E. coli (n = 26) and Salmonella (n = 3) isolates carrying IncF family replicons, ESBL and/or mcr genes were determined for FAB formula. IncF represented the major type of plasmids. Sixteen and eleven Inc groups were identified in E. coli (85.3%) and Salmonella (25.7%), respectively. The predominant replicon patterns between E. coli and Salmonella were IncK-F (23.7%) and IncF (46.2%). Significant correlations (P < 0.05) were observed between plasmid-replicon type and resistance phenotype. Plasmid replicon types were significantly different among sources of isolates and sampling periods. The most common FAB types between E. coli and Salmonella were F2:A-:B- (30.8%) and S1:A-:B- (66.7%), respectively. In conclusion, various plasmids present in E. coli and Salmonella. Responsible and prudent use of antimicrobials is suggested to reduce the selective pressures that favour the spread of AMR determinants. Further studies to understand the evolution of R plasmids and their contribution to the dissemination of AMR genes are warranted.

Companion animals are recognized as potential reservoirs and transmitters of antimicrobial resistance (AMR) within the One Health framework. However, in-depth knowledge on AMR in pet animals remains limited. This study aimed to characterize Salmonella from companion dogs and cats using Whole Genome Sequencing (WGS). A total of 25 Salmonella obtained from clinically healthy household dogs and cats were serotyped and had their antimicrobial susceptibility tested. A discrepancy between the serovars identified by traditional slide agglutination tests and those determined by WGS analysis was observed. The isolates exhibited multidrug resistance (MDR) ( n  = 18) and harbored several resistance genes either chromosomally encoded or plasmid associated. Tn 3 and IS 26 were commonly found flanking AMR genes and class 1 integrons, while an unusual qacL -IS 256 - sul3 arrangement was also frequently observed. Similar AMR genes and insertion sequences were found among dogs and cats from different provinces, suggesting clonal spread and horizontal gene transfer of AMR. The similarity between plasmids (i.e., IncX1 and IncI1 plasmid) carrying AMR genes (e.g., aadA1 , qacL , sul3 , bla TEM-1B , qnrS1 , dfrA , tetA ) in Salmonella from pets in this study and those from other sources (e.g., humans, food producing animals and environment) in different countries was revealed, suggesting that pet dogs and cats may play a significant role in the global spread of AMR. The finding underscores the role of household pets as silent reservoirs of MDR Salmonella and the need for a One Health approach to tackle the issue. Public health campaigns promoting hygiene practices among pet owners should be encouraged. Pet animals should be incorporated into AMR monitoring and surveillance programs as a component of One Health framework.

Background/Objectives: This study assessed the risk associated with third-generation cephalosporin- and fluoroquinolone-resistant Salmonella from pork consumption by integrating phenotypic resistance profiles with genetic data to characterize the risks and transmission pathways. Methods: Salmonella were isolated from raw pork meat samples (n = 793) collected from fresh markets and hypermarkets across Bangkok during 2021–2022, of which 150 were extended-spectrum β-lactamase (ESBL)-producing and 31 were fluoroquinolone-resistant isolates. Phenotypic and genotypic resistance profiles were characterized. Quantitative antimicrobial resistance risk assessment (AMR RA) was conducted using a dose–response model. Results: Salmonella spp. was detected in 42.75% of pork samples, with a higher prevalence in fresh markets (75.5%) than in hypermarket samples and with concentrations ranging from 1.3 to 180 MPN/g. Twenty-eight percent of isolates were ESBL producers, with ciprofloxacin and levofloxacin resistance observed in 5.3% and 3.0%, respectively. The blaCTX-M55 genes were located on conjugative plasmids. Whole genome sequencing revealed both vertical and horizontal gene transfer. IncHI2/N and IncC plasmids shared conserved backbones and resistance gene architectures, indicating horizontal dissemination of resistance genes. Phylogenomics suggested possible clonal transmission among pigs, pork, and humans. AMR RA estimated 88,194 annual illness cases per 100,000 people from ESBL-producing Salmonella and 61,877 from ciprofloxacin-resistant strain, compared with 95,328 cases predicted by QMRA from Salmonella contamination. Cooking pork at ≥64 °C for 3 min eliminated the risk in all scenarios. Sensitivity analysis identified initial contamination level and cooking temperature as key determinants. Conclusions: Raw pork meat consumption represents the highest risk, which can be mitigated by thorough cooking (>64 °C, ≥3 min), while integrating genomic data enhances AMR hazard identification, source attribution, and exposure assessment. Therefore, promoting well-cooked meat consumption and safe cooking practices, alongside the use of AMR genetic data to inform targeted interventions, is recommended.

In Southeast Asia, most antimicrobial resistance (AMR) data on Salmonella have been generated at the phenotypic level, while insights into the genetic characteristics of AMR and virulence genes remain limited. This study aimed to further characterize AMR Salmonella isolates carrying plasmid-associated virulence genes in Thailand and neighboring countries. A total of 366 Salmonella isolates were collected from pigs ( n  = 265), pork ( n  = 69), and humans ( n  = 32) across Thailand, Lao People’s Democratic Republic, Cambodia, and Myanmar. Overall, 69.40% ( n  = 254/366) were multidrug resistant, including resistance to medically important antimicrobials tigecycline, azithromycin, colistin and ciprofloxacin. Whole genome sequencing analysis revealed that five Salmonella Enteritidis ST11 clinical isolates from different patients in different provinces carried IncFIB/IncFII plasmids with plasmid-associated virulence genes ( spvBCD, pefABCD , rck , and mig-5 ), of which three of them (SA615, SA616 and SA617) additionally harbored IncX1 plasmid carrying bla TEM-135 . Virulence plasmids (pSEVTs) exhibited a close relationship with the pSLT of Salmonella Typhimurium LT2 except for two absent segments (PSLT056-PSLT057-PSLT059 PSLT060-PSLT061-PSLT062-PSLT063-064-ssB-PSLT067) and ( traR-traC-trabI-traW-traU trbC-traN-trbE-traF-traQ-traQ-trbB-traH-traD-traH-traI-traX ) as well as two invert regions, R1 (locus tag PSLT001 to repA2 ) and R2 (PSLT025 to finO with deleted tra ) in pSEVTs. None of the plasmids were horizontally transferred under ampicillin selective pressure. Phylogenetic analysis of whole genome sequence and virulence plasmids revealed the clonal dissemination of the isolates. The co-existence of virulence and resistance plasmids may complicate antibiotic therapy, highlighting the need to monitor plasmid-associated virulence genes alongside AMR genes in surveillance programs for humans and animals.

Probiotics have been popularly used in livestock production as an alternative to antibiotics. This study aimed to investigate the microbiological quality and phenotypic and genotypic antimicrobial resistance of bacteria in probiotic products sold for food animals. A total of 45 probiotic products were examined for the number of viable cells, species, and antimicrobial susceptibility; the contamination of Escherichia coli and Salmonella; and the presence of 112 genes encoding resistance to clinically important antimicrobials and transferability of AMR determinants. The results showed that 29 of 45 products (64.4%) were incorrectly labeled in either number of viable cells or bacterial species. None of the tested products were contaminated with E. coli and Salmonella. A total of 33 out of 64 bacterial isolates (51.6%) exhibited resistance to at least one antimicrobial agent. Of the 45 products tested, 16 (35.5%) carried AMR genes. Almost all AMR genes detected in probiotic products were not correlated to the AMR phenotype of probiotic strains formulated in the products. Three streptomycin-resistant Lactobacillus isolates could horizontally transfer their AMR determinants. The findings demonstrated that the probiotic products could serve as reservoirs for the spread of AMR genes and may not yield benefits to animals as claimed. The need for the adequate quality control of probiotic products is highlighted.

Airborne dust in veterinary facilities can act as a reservoir for pathogens and contribute to the spread of antimicrobial resistance (AMR). This study examines airborne bacteria and their resistance profiles in veterinary hospitals and clinics. A total of 179 airborne dust samples were collected from treatment rooms ( = 103) and inpatient wards ( = 76) across 103 veterinary facilities. Total bacterial loads were quantified by direct plate counts and averaged per sample. ESKAPE pathogens, along with Escherichia coli, Salmonella, and Streptococcus, were isolated and assessed for resistance to clinically important antimicrobials, disinfectant minimum inhibitory concentrations (MICs), and plasmid conjugative transfer. Airborne bacterial concentrations varied widely, ranging from 33.37 to 2,881.82 CFU/m . High bacterial loads (>1,000 CFU/m ) were observed in a small proportion of treatment rooms (9.7%) and inpatient wards (9.2%), with mean concentrations of 1,243.8 CFU/m and 1,550.8 CFU/m , respectively. and were the most frequently detected genera (71.8% and 55.3%, respectively), while predominated among Gram-negative bacteria (37.9%). Airborne isolates resistant to clinically important antimicrobials were isolated, including ciprofloxacin-, ceftazidime-, or colistin-resistant ; vancomycin-resistant spp.; meropenem-, imipenem-, levofloxacin-, or tigecycline-resistant spp.; and mupirocin- or cefoxitin-resistant spp. Notably, isolates demonstrated horizontal transfer of ampicillin- and colistin-resistance-encoding plasmids to . MIC distributions for triclosan, chlorhexidine, and benzalkonium chloride were narrow, indicating no or limited reduced susceptibility to these disinfectants. Significant associations between disinfectant MICs and AMR were observed ( < 0.05), supporting potential co-selection and cross-resistance. In , these associations were confined to chlorhexidine and correlated with resistance to certain antibiotics. In Enterococcus, these associations were confined to chlorhexidine and correlated with resistance to certain antibiotics. Indoor airborne dust in veterinary facilities may serve as a potential reservoir of pathogens, posing risks to animal and human health and underscoring the need for strengthened antimicrobial stewardship, infection control, ventilation, and routine AMR bioaerosol surveillance within a One Health framework.

This study aims to investigate bacterial communities and antimicrobial resistance (AMR) in airborne dust from pig farms. Airborne dust, pig feces and feed were collected from nine pig farms in Thailand. Airborne dust samples were collected from upwind and downwind (25 meters from pig house), and inside (in the middle of the pig house) of the selected pig house. Pig feces and feed samples were individually collected from the pen floor and feed trough from the same pig house where airborne dust was collected. A direct total bacteria count on each sampling plate was conducted and averaged. The ESKAPE pathogens together with Escherichia coli, Salmonella , and Streptococcus were examined. A total of 163 bacterial isolates were collected and tested for MICs. Pooled bacteria from the inside airborne dust samples were analyzed using Metagenomic Sequencing. The highest bacterial concentration (1.9–11.2 × 10 3 CFU/m 3 ) was found inside pig houses. Staphylococcus ( n = 37) and Enterococcus ( n = 36) were most frequent bacterial species. Salmonella ( n = 3) were exclusively isolated from feed and feces. Target bacteria showed a variety of resistance phenotypes, and the same bacterial species with the same resistance phenotype were found in airborne dust, feed and fecal from each farm. Metagenomic Sequencing analysis revealed 1,652 bacterial species across all pig farms, of which the predominant bacterial phylum was Bacillota. One hundred fifty-nine AMR genes of 12 different antibiotic classes were identified, with aminoglycoside resistance genes (24%) being the most prevalent. A total of 251 different plasmids were discovered, and the same plasmid was detected in multiple farms. In conclusion, the phenotypic and metagenomic results demonstrated that airborne dust from pig farms contained a diverse array of bacterial species and genes encoding resistance to a range of clinically important antimicrobial agents, indicating the significant role in the spread of AMR bacterial pathogens with potential hazards to human health. Policy measurements to address AMR in airborne dust from livestock farms are mandatory.

Background and Aim: The genetic relationship among serotypes of Salmonella enterica from food animals, food of animal origin, and human is of interest as the data could provide an important clue for the source of human infection. This study aimed to determine the genetic relatedness of S. enterica from pig production and human in Thailand-Laos border provinces. Materials and Methods: A total of 195 S. enterica serotypes isolated from pig and pork (n=178) and human (n=17) including four serotypes (Typhimurium, Rissen, Derby, and Stanley) were randomly selected to examine their genetic relatedness using highly conserved sequence of three genes (fim A, man B, and mdh). Results: The results showed that 195 Salmonella isolates of four different serotypes were grouped into five different clusters, and members of the same Salmonella serotypes were found in the same cluster. Salmonella isolated from pig production and human in Thailand-Laos border provinces represented overlapping population and revealed a high degree of similarity, indicating close genetic relationship among the isolates. Conclusion: The results support that the determination of Salmonella serotyping combined with analysis of phylogenetic tree can be used track the clonal evolution and genetic diversity of Salmonella serotypes in different host species.

This study aimed to investigate the potential mechanisms associated with the persistence of chloramphenicol (CHP) resistance in Escherichia coli and Salmonella enterica isolated from pigs, pork, and humans in Thailand. The CHP-resistant E. coli (n = 106) and Salmonella (n = 57) isolates were tested for their CHP susceptibility in the presence and absence of phenylalanine arginine β-naphthylamide (PAβN). The potential co-selection of CHP resistance was investigated through conjugation experiments. Whole genome sequencing (WGS) was performed to analyze the E. coli (E329, E333, and E290) and Salmonella (SA448, SA461, and SA515) isolates with high CHP MIC (32-256 μg/mL) and predominant plasmid replicon types. The presence of PAβN significantly reduced the CHP MICs (≥4-fold) in most E. coli (67.9%) and Salmonella (64.9%). Ampicillin, tetracycline, and streptomycin co-selected for CHP-resistant Salmonella and E. coli-transconjugants carrying cmlA. IncF plasmids were mostly detected in cmlA carrying Salmonella (IncFIIAs) and E. coli (IncFIB and IncF) transconjugants. The WGS analysis revealed that class1 integrons with cmlA1 gene cassette flanked by IS26 and TnAs1 were located on IncX1 plasmid, IncFIA(HI1)/HI1B plasmids and IncFII/FIB plasmids. IncFIA(HI1)/HI1B/Q1in SA448 contained catA flanked by IS1B and TnAs3. In conclusion, cross resistance through proton motive force-dependent mechanisms and co-selection by other antimicrobial agents involved the persistence of CHP-resistance in E. coli in this collection. Dissemination of CHP-resistance genes was potentially facilitated by mobilization via mobile genetic elements.