Resistance to the last-line antibiotics against invasive Gram-negative bacterial infection is a rising concern in public health. Multidrug resistant (MDR) Acinetobacter baumannii Aci46 can resist colistin and carbapenems with a minimum inhibitory concentration of 512 µg/mL as determined by microdilution method and shows no zone of inhibition by disk diffusion method. These phenotypic characteristics prompted us to further investigate the genotypic characteristics of Aci46. Next generation sequencing was applied in this study to obtain whole genome data. We determined that Aci46 belongs to Pasture ST2 and is phylogenetically clustered with international clone (IC) II as the predominant strain in Thailand. Interestingly, Aci46 is identical to Oxford ST1962 that previously has never been isolated in Thailand. Two plasmids were identified (pAci46a and pAci46b), neither of which harbors any antibiotic resistance genes but pAci46a carries a conjugational system (type 4 secretion system or T4SS). Comparative genomics with other polymyxin and carbapenem-resistant A. baumannii strains (AC30 and R14) identified shared features such as CzcCBA, encoding a cobalt/zinc/cadmium efflux RND transporter, as well as a drug transporter with a possible role in colistin and/or carbapenem resistance in A. baumannii. Single nucleotide polymorphism (SNP) analyses against MDR ACICU strain showed three novel mutations i.e., Glu229Asp, Pro200Leu, and Ala138Thr, in the polymyxin resistance component, PmrB. Overall, this study focused on Aci46 whole genome data analysis, its correlation with antibiotic resistance phenotypes, and the presence of potential virulence associated factors.

Salmonella contamination in the food chain is a common root of foodborne outbreaks. The transmission of antimicrobial resistance among Salmonella and food bacteria raises global public health concern. As a major food exporter and travel hub in Southeast Asia, Thailand is particularly susceptible. To better understand the circulating Salmonella , we characterized 74 non-typhoidal Salmonella isolates previously obtained from Thailand food markets. Whole genome sequencing, drug susceptibility testing, and host invasion efficiency assays were performed. The most prevalent serotype was Salmonella serotype Rissen (32.43%) followed by Derby (12.16%). Fifty-two isolates were multidrug-resistant (MDR), with their primary resistance pattern being ampicillin, streptomycin, and tetracycline resistance. The most resistant strain was S . Rissen exhibiting resistance to 13 tested drugs, including third-generation cephalosporin. Six cephalosporin-resistant isolates were identified, four of which were extended-spectrum β-lactamase (ESBL)-producing strains harboring the bla _CTX-M-14 or bla _CTX-M-55 ESBL gene. Complete genomes showed that three ESBL-producing isolates contained plasmid-mediated ESBL, and the other was chromosomal-mediated. In vitro invasion efficiencies of ESBL-producing strains into mucous-producing human colorectal adenocarcinoma HT29-MTX-E12 cells were compared to the reference strain Salmonella Typhimurium LT2. Statistically significant higher invasion efficiency in the chromosomal-mediated ESBL strain was found. Interestingly, the ESBL plasmid detected during this study was highly similar to a plasmid previously isolated from a Thai patient. This study highlights that the majority of Salmonella isolated from Thai foods are MDR and potentially ESBL-producing strains, highlighting the need for continued surveillance and intervention strategies. IMPORTANCE: In Thailand, fermented foods are typically consumed raw, and pork is considered a delicacy of Thai cuisine. The presence of multidrug resistant (MDR) foodborne pathogens in these food types raises concern and presents a risk to public health. Here, we report that Salmonella Rissen was the most prevalent serotype isolated from these food samples in Thailand. All isolates carried virulence gene clusters crucial for pathogenesis, and more than 70% of isolates were MDR strains. Four of the MDR strains were ESBL-producing. Whole genome sequence analysis and phenotypic characterizations revealed that chromosome-mediated ESBL strains possessed higher in vitro invasion efficiency than plasmid-mediated ESBL strains. This study highlights two key public health threats: the risk of acquiring difficult-to-treat MDR Salmonella infections from undercooked food and the circulation of AMR plasmids in fresh markets in Thailand.

Vibrio parahaemolyticus (VP) is a major bacterial species that causes early mortality syndrome (EMS) in shrimps. EMS can be classified into two groups based on histological signs of hepatopancreatic tissues, i.e., acute hepatopancreatic necrosis disease (AHPND) and non‐AHPND. To investigate how toxin‐producing AHPND and toxin‐lacking non‐AHPND VP could lead to EMS, growth characteristics and transcriptomic analyses of the representative strains, 5HP and 2HP, were compared. Non‐pathogenic VP represented by strain S02 was also used. Two types of growth media included rich medium represented by tryptic soy broth plus 1.5% NaCl (TSB) and depleted media represented by artificial seawater (SW) and spent seawater (SSW). SSW refers to a sterile used‐SW medium from healthy shrimp rearing or shrimp‐conditioned SW. Growth characteristics under these media indicated that TSB and SSW supported better growth than SW, suggesting shrimp‐conditioned SW is sufficient to support normal VP growth. Transcriptomic analyses revealed that both EMS isolates shared overall expression patterns. Metabolic stress adaptation systems of non‐AHPND strain 2HP under SW and SSW were more upregulated than in AHPND strain 5HP. Specific virulence genes (i.e., zot1 [zonula occludens toxin] and vopS [type III secretion effector]) and a general stress response gene (i.e., rpoS [stress response sigma factor]) were upregulated in strain 2HP under both SW and SSW. These expression profiles of strain 2HP suggest higher persistence, which might be useful for cell survival and non‐AHPND pathogenesis even without toxin production. We proposed that these genes encode virulence factor ‘candidates’ in non‐AHPND VP.

The presence of antibiotic-resistant Escherichia coli in food is a serious and persistent problem worldwide. In this study, 68 E. coli strains isolated from Thai food samples were characterized. Based on antibiotic susceptibility assays, 31 of these isolates (45.59%) showed multiple antibiotic resistance (MAR) index values > 0.2, indicating high exposure to antibiotics. Among these, strain CM24E showed the highest resistance (it was resistant to ten antibiotics, including colistin and imipenem). Based on genome sequencing, we identified four isolates (namely, CF25E, EF37E, NM10E1, and SF50E) with novel Achtman-scheme multi-locus sequence types (STs) (ST14859, ST14866, ST14753, and ST14869, respectively). Clermont phylogrouping was used to subtype the 68 researched isolates into five Clermont types, mainly A (51.47%) and B1 (41.18%). The bla_EC gene was found only in Clermont type A, while the bla_EC-13 gene was predominant in Clermont type B1. A correlation between genotypes and phenotypes was found only in Clermont type B1, which showed a strong positive correlation between the presence of an afa operon and yersiniabactin-producing gene clusters with the colistin resistance phenotype. Strain SM47E1, of Clermont type B2, carried the highest number of predicted virulence genes. In summary, this study demonstrates the pressing problems posed by the prevalence and potential transmission of antimicrobial resistance and virulence genes in the food matrix.