Analysis of Antimicrobial Resistance in Non-typhoidal Salmonella Collected From Pork Retail Outlets and Slaughterhouses in Vietnam Using Whole Genome Sequencing

A review and meta-analysis of non-typhoidal Salmonella in Vietnam: Challenges to the control and antimicrobial resistance traits of a neglected zoonotic pathogen

Non-typhoidal Salmonella (NTS) is a food-borne zoonotic pathogen with important implications for human health. Despite its importance, the burden of NTS infections in Vietnam is unknown. We conducted a systematic review and a meta-analysis to describe the prevalence and phenotypic antimicrobial resistance (AMR) for NTS over time in Vietnam. Following PRISMA guidelines, we identified 72 studies from PubMed and Google Scholar containing data relevant to 'Salmonella', 'Salmonellosis', and 'Vietnam', or 'Viet Nam'. Of those, forty-two papers reporting prevalence of NTS, and twenty-six including data on phenotypic resistance were selected for meta-analysis. The prevalence of NTS ranged from 2% to 5% in humans and from 30% to 41% in samples from animals and the farm/slaughterhouse environment. Between 2000 and 2020 we observed a 27.3% (p = 0.044) increase in absolute terms in prevalence among individuals with enteric diseases and a 12.0% (p = 0.047) increase in aquaculture/seafood samples. The most commonly serovars identified across studies included S. Weltevreden (12.0%), followed by S. Typhimurium (10.1%), S. Derby (6.4%), S. London (5.8%), S. Anatum (4.4%), S. Rissen (3.9%), S. Enteritidis (3.7%), S. Albany (3.3%) and S. 4,[5],12:i:- (3.0%). Over the same period, there was an increasing trend in the pooled AMR prevalence for quinolones (15.6% relative increase), 3rd-, 4th-, and 5th-generation cephalosporins (23.7%), penicillins (16.1%), tetracyclines (12.9%), sulfonamides (8.8%), amphenicol (17.8%), and multidrug resistance (11.4%) (all p ≤ 0.014). A broad range of AMR genes (ARGs) were detected in both human and animal populations. The observed prevalence and AMR trends in Vietnam underscore the need of adopting a One Health strategy encompassing surveillance systems, research initiatives, and awareness campaigns to effectively address the challenges posed by NTS.

Prevalence and genetic characteristics of Salmonella enterica serovar Meleagridis from animals and humans

Salmonella enterica serovar Meleagridis (S. Meleagridis) is a non-typhoidal Salmonella serotype commonly found in food and humans. In this study, we investigated 61 Chinese S. Meleagridis isolates from various sources, predominantly from pigs and pig products. Additionally, the serotype was also identified in samples from human infections. Whole-genome sequencing analysis of these isolates, combined with 10 isolates from other countries, demonstrated that the Chinese isolates formed a distinct Cluster C, further divided into two subclusters (Cluster C-1 and Cluster C-2) based on cgMLST analysis. CRISPR typing divided the 61 isolates into three CRISPR types (MCT1, MCT2, MCT3), belonging to Cluster I (96.7%, 59/61) and Cluster II (3.3%, 2/61), which corresponded to Cluster C-2 and Cluster C-1, respectively. Among the 48 identified spacers, the spacer SoeB5 was the only target differentiating MCT1 and MCT2 isolates of Cluster I. MelB12 and MelB13, identified in US and Denmark isolates, were not found among the 61 Chinese isolates. Examination of antimicrobial resistance gene profiles and their genetic contexts uncovered the presence of IncR plasmids in 43 (70.5%, 43/61) isolates within Cluster C, conferring resistance to tetracycline and trimethoprim/sulfamethoxazole. Homology analysis of spacers showed that 12 spacers exhibited similarity to sequences in phages or plasmids. Additionally, five spacers showed homology to sequences in plasmids from other Salmonella serotypes, suggesting their potential role in helping S. Meleagridis resist against Salmonella isolates carrying similar plasmids. The comprehensive analysis of CRISPR, cgMLST, and antimicrobial resistance in S. Meleagridis highlights the pig reservoir as a crucial factor in the evolution and transmission of this serotype to humans.

Bacterial profile of pork from production to retail based on high-throughput sequencing

Pork is a common vehicle for foodborne pathogens, including Salmonella spp. and Yersinia enterocolitica. Cross-contamination can occur at any stage of the pork production chain, from farm to market. In the present study, high-throughput sequencing was used to characterize bacterial profiles and track their changes along the whole supply chain. Tracked meat samples (pig on the farm, carcass in the slaughterhouse, unprocessed carcass and processed meat in the processing plant, and fresh pork at the local retail stores) and their associated environmental samples (e.g., water, floor, feed, feces, and workers' gloves) were collected from sequential stages (n = 96) and subjected to 16S rRNA metataxonomic analyses. At the farm, a total of 652 genera and 146 exclusive genera were identified in animal and environmental samples (pig, drain, floor, fan, and feces). Based on beta diversity analysis, it was demonstrated that the microbial composition of animal samples collected at the same processing step is similar to that of environmental samples (e.g., drain, fan, feces, feed, floor, gloves, knives, tables, and water). All animal and environmental samples from the slaughterhouse were dominated by Acinetobacter (55.37 %). At the processing plant, belly meat and neck meat samples were dominated by Psychrobacter (55.49 %). At the retail level, key bacterial players, which are potential problematic bacteria and important members with a high relative abundance in the samples, included Acinetobacter (8.13 %), Pseudomonas (6.27 %), and Staphylococcus (2.13 %). In addition, the number of confirmed genera varied by more than twice that identified in the processing plant. Source tracking was performed to identify bacterial contamination routes in pork processing. Animal samples, including the processing plant's carcass, the pig from the farm, and the unwashed carcass from the slaughterhouse (77.45 %), along with the processing plant's gloves (5.71 %), were the primary bacterial sources in the final product. The present study provides in-depth knowledge about the bacterial players and contamination points within the pork production chain. Effective control measures are needed to control pathogens and major pollutants at each stage of pork production to improve food safety.

Speaking the host language: how Salmonella effector proteins manipulate the host

Salmonella injects over 40 virulence factors, termed effectors, into host cells to subvert diverse host cellular processes. Of these 40 Salmonella effectors, at least 25 have been described as mediating eukaryotic-like, biochemical post-translational modifications (PTMs) of host proteins, altering the outcome of infection. The downstream changes mediated by an effector's enzymatic activity range from highly specific to multifunctional, and altogether their combined action impacts the function of an impressive array of host cellular processes, including signal transduction, membrane trafficking, and both innate and adaptive immune responses. Salmonella and related Gram-negative pathogens have been a rich resource for the discovery of unique enzymatic activities, expanding our understanding of host signalling networks, bacterial pathogenesis as well as basic biochemistry. In this review, we provide an up-to-date assessment of host manipulation mediated by the Salmonella type III secretion system injectosome, exploring the cellular effects of diverse effector activities with a particular focus on PTMs and the implications for infection outcomes. We also highlight activities and functions of numerous effectors that remain poorly characterized.

Colistin resistance and resistance determinants are mobile among Salmonella enterica isolates from diseased and healthy pigs in Thailand

Salmonella is an important enteric pathogen that poses a threat to human and livestock animal health, with emerging multidrug resistance (MDR) a major public health issue globally. We investigated the prevalence of Salmonella in healthy and diseased pigs from Thai pig farms and determined their phenotypic and genotypic antimicrobial resistance profiles. A total of 150 fecal samples were collected from pigs housed in pens from four separate pig farms in southern Thailand and tested for the presence of Salmonella. Confirmed Salmonella isolates were tested for their susceptibility to 11 antimicrobials, and PCR used to detect known antimicrobial resistance genes (ARGs). Salmonella isolates were cultured from 69% (103/150) of all fecal samples, with higher prevalence in disease pigs (12/15; 80%), compared with healthy pigs (91/135; 67%). Serotype Rissen was the most frequently identified serotype among the Salmonella isolates. Resistance to ampicillin (AMP) (97%), sulfonamide-trimethoprim (SXT) (97%), and tetracycline (TET) (94%) were the most common phenotypes observed. The most common ARGs identified were blaTEM gene (99.%), tetA (87%), sul1 (77%), and dfrA1 (74%), and more than 95% of the Salmonella isolates tested were MDR - based on resistance to three or more antimicrobial classes. The most common antimicrobial resistance pattern exhibited was AMP-TET-SXT (76%), and resistance to colistin (via the mcr-1 gene) was observed in both healthy and diseased pigs. The clonal groups of PFGE analysis in serotype Typhimurium revealed the genetic relationship among Salmonella isolated from healthy and diseased pigs from different pig farms.

A systematic review and meta-analysis of integrated studies on antimicrobial resistance in Vietnam, with a focus on Enterobacteriaceae, from a One Health perspective

Vietnam is a low- and middle-income country (LMIC), a primary food producer, and an antimicrobial resistance (AMR) hotspot. AMR is recognized as a One Health challenge since it may transfer between humans, animals and the environment. This study aimed to apply systematic review and meta-analysis to investigate the phenotypic profiles and correlations of antimicrobial-resistant Enterobacteriaceae across three compartments: humans, animals and the environment in Vietnam. A total of 89 articles found in PubMed, Science Direct, and Google Scholar databases were retrieved for qualitative synthesis. E. coli and non-typhoidal Salmonella (NTS) were the most common bacterial species in studies of all compartments (60/89 studies). Among antimicrobials classified as critically important, the resistance levels were observed to be highest to quinolones, 3rd generation of cephalosporins, penicillins, and aminoglycosides. Of 89 studies, 55 articles reported the resistance prevalence of E. coli and NTS in healthy humans, animals and the environment against ciprofloxacin, ceftazidime, ampicillin, gentamicin, sulfamethoxazole-trimethoprim, chloramphenicol was used for meta-analysis. The pooled prevalence was found highest in E. coli against ampicillin 84.0% (95% CI 73.0-91.0%) and sulfamethoxazole-trimethoprim 66.0% (95% CI 56.0-75.0%) while in NTS they were 34.0% (95% CI 24.0-46.0%), 33.0% (95% CI 25.0-42.0%), respectively. There were no significant differences in the pooled prevalence of E. coli and NTS to these antimicrobials across healthy humans, animals and the environment, except for ceftazidime-resistant E. coli (χ² = 8.29, p = 0.02), chloramphenicol-resistant E.coli (χ² = 9.65, p < 0.01) and chloramphenicol-resistant NTS (χ² = 7.51, p = 0.02). Findings from the multiple meta-regression models indicated that the AMR levels in E. coli (β = 1.887, p < 0.001) and the North (β = 0.798, p = 0.047) had a higher fraction of AMR than NTS and other regions of Vietnam. The outcomes of this study play an important role as the baseline information for further investigation and follow-up intervention strategies to tackle AMR in Vietnam, and more generally, can be adapted to other LMICs.