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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 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., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Puangseree et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

The impact of antimicrobial resistance (AMR) on global public health has been widely documented. AMR in the environment poses a serious threat to both human and animal health but is frequently overlooked. This study aimed to characterize the association between phenotype and genotype of AMR, virulence genes and Extended-Spectrum β-Lactamase (ESBL) production from estuarine environment. The Salmonella (n = 126) and E. coli (n = 409) were isolated from oysters and estuarine water in Thailand. The isolates of Salmonella (96.9%) and E. coli (91.4%) showed resistance to at least one antimicrobial agent. Multidrug resistance (MDR) was 40.1% of Salmonella and 23.0% of E. coli. Resistance to sulfamethoxazole was most common in Salmonella (95.2%) and E. coli (77.8%). The common resistance genes found in Salmonella were sul3 (14.3%), followed by blaTEM (11.9%), and cmlA (11.9%), while most E. coli were blaTEM (31.5%) and tetA (25.4%). The ESBL production was detected in Salmonella (1.6%, n = 2) of which one isolate was positive to blaTEM-1. Eight E. coli isolates (2.0%) were ESBL producers, of which three isolates carried blaCTX-M-55 and one isolate was blaTEM-1. Predominant virulence genes identified in Salmonella were invA (77.0%), stn (77.0%), and fimA (69.0%), while those in E. coli isolates were stx1 (17.8%), lt (11.7%), and stx2 (1.2%). Logistic regression models showed the statistical association between resistance phenotype, virulence genes and ESBL production (p < 0.05). The findings highlighted that estuarine environment were potential hotspots of resistance. One Health should be implemented to prevent AMR bacteria spreading., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Jeamsripong et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

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.

Introduction. Antimicrobial resistance (AMR) is a One Health issue concerning humans, animals and the environment and a unified One Health approach is required to contain this problematic issue. Dogs and cats are popular pet animals and are known to carry many bacterial pathogens that are of public health importance, including Salmonella . However, data on AMR in companion animals is limited. Gap statement. Scant AMR data from bacteria originating from companion animals limits an accurate assessment of the impacts of pet-animal-related AMR on public health. Purpose. This study aimed to phenotypically and genetically investigate AMR in Salmonella isolated from pet dogs and cats in Thailand. Methodology. Salmonella enterica were isolated from pet dogs ( n =159) and cats ( n =19) in Thailand between 2016 and 2019. All isolates were serotyped. Phenotypic and genotypic antimicrobial resistance was examined. PCR-based replicon typing, replicon sequence typing and plasmid multilocus sequence typing were conducted to characterize plasmids. Results. Seventy-seven serovars were identified, with serovars Weltevreden (9.6%) and Stockholm (9.0%) the most common. Most of the isolates (34.3%) were multidrug-resistant. The serovar Stockholm was an ESBL-producer and carried the β-lactamase genes bla TEM-1 and bla CTX-M-55 . The plasmid-mediated quinolone resistance (PMQR) gene, qnrS, was also detected (10.1%). Class 1 integrons carrying the dfrA12-aadA2 cassette array were most frequent (45.9%). Five plasmid replicon types as IncA/C (0.6%), N (1.1%), IncFIIA (28.7%), IncHI1 (2.2%), and IncI1 (3.4%) were identified. Based on the pMLST typing scheme ( n =9), plasmids were assigned into five different STs including IncA/C-ST6 ( n =1), IncH1-ST16 ( n =4), IncI1-ST3 ( n =1), IncI1-ST60 ( n =1) and IncI1-ST136 ( n =1). The ST 16 of IncHI1 plasmid was a novel plasmid ST. Subtyping F-type plasmids using the RST scheme ( n =9) revealed four different combinations of replicons including S1:A-:B- ( n =4), S1:A-:B22 ( n =2), S3:A-:B- ( n strains with different R plasmid. The implementation of AMR phenotypes instigation and genotypic monitoring and surveillance programmes in companion animals are imperative as integral components of the One Health framework.n =1). Conclusions. Our findings highlight the role of clinically healthy household dogs and cats as carriers of AMR Salmonella strains with different R plasmid. The implementation of AMR phenotypes instigation and genotypic monitoring and surveillance programmes in companion animals are imperative as integral components of the One Health framework.

Salmonella enterica isolates (n = 122), including 32 serotypes from 113 dogs and 9 cats, were obtained from household dogs (n = 250) and cats (n = 50) during 2012-2015. The isolates were characterized by serotyping, antimicrobial resistance phenotyping and genotyping, and virulence gene screening. Serovars Weltevreden (15.6%) and Typhimurium (13.9%) were the most common. The majority (43%) of the isolates were multidrug resistant. The dog isolates (12.3%) harbored class 1 integrons, of which the dfrA12 - aadA2 cassette was most frequent (66.7%). The only class integron in serovar Albany was located on a conjugative plasmid. Two ESBL-producing isolates ( i.e ., a serovar Krefeld and a serovar Enteritridis) carried bla TEM and bla CTX-M , and the bla TEM gene in both was horizontally transferred. Of the plasmid-mediated quinolone resistance genes tested, only qnrS (4.9%) was detected. Most Salmonella isolates harbored invA (100%), prgH (91.8%), and sipB (91%). Positive associations between resistance and virulence genes were observed for bla PSE-1 / orgA , cmlA / span , tolC , and sul1 / tolC ( p ＜ 0.05). The results suggest that companion dogs and cats are potential sources of S. enterica strains that carry resistance and virulence genes and that antimicrobial use in companion animals may select for the examined Salmonella virulence factors.

This study aimed to examine the prevalence and antimicrobial resistance (AMR) of Salmonella isolates from broiler chickens, pigs and their associated meat products in the Thailand-Cambodia border provinces. A total of 941 samples were collected from pigs and broiler chickens at slaughter houses and from carcasses at local fresh markets in Sa Kaeo, Thailand (n = 554) and Banteay Meanchey, Cambodia (n = 387) in 2014 and 2015. From these samples, 345 Salmonella isolates were collected from Sa Keao (n = 145; 23%) and Banteay Meanchey (n = 200; 47%) and assayed for antimicrobial susceptibility, class 1 integrons and extended-spectrum β-lactamase (ESBL) genes. Serovars Typhimurium (29%) and Rissen (29%) were the most common serotypes found in Thai and Cambodian isolates, respectively. Multidrug resistance was detected in 34% and 52% of isolates from Sa Keao and Banteay Meanchey, respectively. The majority of the Thai isolates were resistant to ampicillin (72.4%), whereas most Cambodian isolates were resistant to sulfamethoxazole (71%). Eleven isolates from Sa Keao and 44 from Banteay Meanchey carried class 1 integrons comprising resistance gene cassettes. The most common gene cassette array was dfrA12-aadA2 (61.1%). Six isolates were ESBL producers. The β-lactamase genes found included bla TEM-1 , bla CTX-M-55 and bla CMY-2 . Some of these class 1 integrons and ESBL genes were located on conjugative plasmid. In conclusion, multidrug-resistant Salmonella are common in pigs, chickens and their products in the Thailand-Cambodia border provinces. Our findings indicate that class 1 integrons play a role in spread of AMR in the strains in this study., (© 2017 The Societies and John Wiley & Sons Australia, Ltd.)

A total of 221 Salmonella enterica from raw pork (n=64), raw chicken (n=80), and humans (n=77) were characterized for antimicrobial resistance phenotypes and genotypes and virulence plasmid-associated genes. Most Salmonella isolates (95.9%) were multidrug resistant and exhibited high resistance to sulfamethoxazole (96.4%), streptomycin (93.2%), spectinomycin (76.5%), tetracycline (73.3%), ampicillin (70.1%), and trimethoprim (60.2%). Forty-one percent of all isolates were intI1-positive, of which 60% carried class 1 integrons with variable region ranging in size from 0.2 to 2.0 kb. Six integron profiles (IP-I to IP-VI) were defined. The dfrA12-aadA2 cassette was most prevalent (66.7%). Class 1 integrons with the dfrA12-aadA2 cassette in five pork isolates could be horizontally transferred. Three pork isolates carried Salmonella genomic island 1 (SGI1), of which a serovar Anatum harbored SGI1 gene cluster located between thdF and int2. Two single-point mutations (i.e., G-259-T and C-248-T) in gyrA leading to Asp-87-Tyr and Ser-83-Phe substitutions in GyrA, respectively, were detected. Of all plasmid-mediated quinolone resistance genes tested, only qnrS (4.1%) and qnrB (1.8%) were found. The virulence plasmid-associated genes including spvC, pefA, and rck were identified in 8.1%, 1.8%, and 1.4% of all Salmonella isolates, respectively.

One hundred and eighty-nine Salmonella isolates from swine were tested for susceptibility to nine antimicrobial agents, presence of dfrA12 and class 1 integrons containing dfrA12-orfF-aadA2 cassette. All isolates were multidrug resistant and exhibited highest resistance prevalence to trimethoprim (93%). Most isolates (89%) were intll-positive and 107 isolates (57%) carried dfrA12, all of which were resistant to trimethoprim. Forty-eight dfrA12-harboring strains (45%) were intl1-positive together with dfrA12-aadA2 gene cassette. Fifteen isolates contained dfrA12 but not intl1 and dfrA12-aadA2 cassette. The results indicated a wide distribution of dfrA12 and its role in dissemination of trimethoprim resistance among Salmonella isolates from fattening pigs.

In this study, 183 Salmonella enterica isolates were characterised for integrons and virulence genes. Among the isolates, 46% were positive for intI1, but no isolates carried intI2 or intI3. Eighteen class 1 integrons (21%) contained resistance gene cassettes (i.e. dfrA1-orfC, dfrA12-aadA2, bla(PSE-1) and aadA2) and five class 1 integrons with the dfrA12-aadA2 array were conjugally transferable. Two Salmonella pork isolates of serotypes Albany and Kedougou possessed Salmonella genomic island 1 variants SGI1-G and SGI1-F, respectively. Four class 1 integrons contained an atypical 3'-CS linked to the qacH-sul3 domain, and three were not a sul type. Two novel GyrA mutations (Pro-45→Ser and Met-48→Ile) and three novel ParC mutations (Ser-5→Arg, Thr-31→Met and Leu-77→Arg) were identified in ciprofloxacin-resistant isolates. At least 90% of the Salmonella isolates contained pagC, prgH, sitC, sipB or spaN, whereas all isolates harboured invA, msgA, spiA and tolC., (Copyright © 2011 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.)

One hundred sixty Salmonella enterica isolates from clinically healthy dairy cows were assayed for antibiotic susceptibilities, the presence of class 1 integrons, antimicrobial resistance genes and virulence genes, and conjugal transfer of antimicrobial resistance determinants. One hundred nine (68%) of the Salmonella isolates were resistant to at least 1 antibiotic, and 14 isolates (9%) were multiresistant. The most prevalent resistance observed was to streptomycin (64%). Class 1 integrons were detected in only two Salmonella isolates (serovar Singapore and Derby), and both integrons harbored the same cassette content aadA2. The Derby class 1 integrons were associated with Salmonella genomic island 1-A. Most commonly found resistance genes were strA and strB (9.2%). None of class 1 integrons were horizontally transferred, and the resistance genes were successfully transferred from six (5.5%) Salmonella strains. One hundred fifty-nine isolates (98.8%) were positive to the invasion gene invA, whereas the virulence plasmid-associated genes spvC and pefA were found in only two (1.3%) and one (0.6%) Salmonella isolates, respectively.

A total of 184 resistant Salmonella enterica isolated from poultry and swine were investigated for the distribution of and associations between various antimicrobial resistance genes. All the isolates were screened for the presence of class 2 and 3 integrase genes and 18 resistance genes corresponding to their resistance phenotypes. None of the isolates carried class 2 and 3 integrons. The investigated resistance genes were responsible for resistance in 78% of the isolates. All the strains harboring more than one resistance gene were resistant to three or more antimicrobials. The bla(TEM), cmlA, tetA, dfrA12, sul3, aadA1 genes were detected in the majority of strains resistant to ampicillin (87%), chloramphenicol (63%), tetracycline (60%), trimethoprim (42%), sulphonamides (42%) and streptomycin/spectinomycin (61%), respectively. Two ciprofloxacin-resistant isolates had a single point mutation leading to Ser-83-Phe in GyrA or Thr-57-Ser in ParC. Statistical analysis revealed good correlation between the presence of antimicrobial resistance genes and corresponding resistance phenotype (p<0.01). The results indicated that the resistance genes play a major role in conferring resistance among the Salmonella isolates investigated.

Salmonella enterica isolates from poultry (n=125) and swine (n=132) in Thailand were investigated for antibiotic resistance, susceptibility to disinfectants (benzalkonium chloride (BKC), chlorhexidine digluconate (CHX), zinc chloride and copper sulfate) and cyclohexane tolerance. Forty-two percent were of multiple resistance to antibiotics. The minimum inhibitory concentrations (MICs) of all antibiotics against isolates from swine were higher than that against the isolates from poultry. There were generally few variations in MICs to all disinfectants, indicating that the isolates had either no or only a limited degree of developed resistance to the disinfectants tested. Only 5 isolates (1.9%) were tolerant to cyclohexane. The proton-dependent efflux systems did not play a major role in the reduced susceptibility to BKC and CHX, since susceptibility was not restored when an efflux inhibitor, carbonyl cyanide m-chlorophenylhydrazone (CCCP) was present. Successive exposure to subinhibitory concentrations of BKC and CHX generated mutants resistant to BKC and CHX. A spontaneous BKC-resistant derivative expressed cross-resistance to antibiotics, chloramphenicol and erythromycin. The mechanism responsible for cross-resistance between BKC and antibiotics was not driven by the proton motif force (PMF).

The unusual 3' conserved sequence region of class 1 integrons was characterized in seven Salmonella isolates from swine and poultry. Three types of gene cassette arrays, aadA2-cmlA1-aadA1, sat-psp-aadA2-cm1A1-aadA1 and drfA12-orf-aadA2-cmlA1-aadA1, were found to be linked to a genetic organization qacH-IS440-sul3. All class 1 integrons were located on a conjugative plasmid that could be transferred to Escherichia coli. The results support the notion that the use of an antibiotic can select for resistance not only to that specific agent, but also to other unrelated antimicrobials including those that are no longer approved for use in food animal production.

Two hundred eleven Salmonella enterica strains representing 35 serotypes isolated from healthy poultry (n=103) and swine (n=108) were used in this study. The occurrence and characteristics of class 1 integrons were investigated. Salmonella genomic islands (SGIs) and the horizontal transfer of integrons were assessed. One hundred eighty-six isolates (88%) were resistant to at least one antimicrobial and 140 isolates (66%) were multidrug resistant. The intI1 gene was present in 54 isolates (25.6%), of which 33 (15.6%) carried gene cassettes with sizes ranging from 0.7 to 2.3 kb. Sequence analysis revealed 11 distinct integron profiles in which resistance genes bla(PSE-1), dfrA1, dfrA12, aadA2, aadA4a, and silB were present. The gene cassette array dfrA12-aadA2 was the most prevalent among the isolates whereas most integrons were located on conjugative plasmids. SGI1 variants (SGI1-A and -F) were present in nine isolates belonging to serovars Albany, Emek, Kedougou, and Kingston.

In this study, a total of 122 Salmonella enterica isolates from poultry and swine were assessed for susceptibility to clinically important antibiotics and to benzalkonium chloride (BKC). All isolates were examined for the presence of the antiseptic resistance genes qacE and qacEDelta1 and intl1 (class 1 integrase). The intl1-positive strains were further investigated for the presence of the 3' conserved region. The results demonstrated widespread distribution of qacEDelta1 (27%) but no isolate with qacE was observed. The intl1 gene was identified in 23 isolates (70%) with qacEDelta1. All of the intl1-postive strains carried qacEDelta1 in 3' conserved segment, confirming that the qacEDelta1 gene is linked to the integrons. Increased MIC value to BKC was independent of the presence of qacEDelta1, and multiple antibiotic-resistant bacteria were no more tolerant to BKC than the non-multidrugresistant strains, regardless of the presence of qacEDelta1.