Prediction of Phenotypic Antimicrobial Resistance Profiles From Whole Genome Sequences of Non-typhoidal Salmonella enterica

Clonal background and routes of plasmid transmission underlie antimicrobial resistance features of bloodstream Klebsiella pneumoniae

Bloodstream infections caused by the opportunistic pathogen Klebsiella pneumoniae are associated with adverse health complications and high mortality rates. Antimicrobial resistance (AMR) limits available treatment options, thus exacerbating its public health and clinical burden. Here, we aim to elucidate the population structure of K. pneumoniae in bloodstream infections from a single medical center and the drivers that facilitate the dissemination of AMR. Analysis of 136 short-read genome sequences complemented with 12 long-read sequences shows the population consisting of 94 sequence types (STs) and 99 clonal groups, including globally distributed multidrug resistant and hypervirulent clones. In vitro antimicrobial susceptibility testing and in silico identification of AMR determinants reveal high concordance (90.44-100%) for aminoglycosides, beta-lactams, carbapenems, cephalosporins, quinolones, and sulfonamides. IncF plasmids mediate the clonal (within the same lineage) and horizontal (between lineages) transmission of the extended-spectrum beta-lactamase gene blaCTX-M-15. Nearly identical plasmids are recovered from isolates over a span of two years indicating long-term persistence. The genetic determinants for hypervirulence are carried on plasmids exhibiting genomic rearrangement, loss, and/or truncation. Our findings highlight the importance of considering both the genetic background of host strains and the routes of plasmid transmission in understanding the spread of AMR in bloodstream infections.

Genetic diversity of Listeria monocytogenes from seafood products, its processing environment, and clinical origin in the Western Cape, South Africa using whole genome sequencing

Listeria monocytogenes is a concern in seafood and its food processing environment (FPE). Several outbreaks globally have been linked to various types of seafood. Genetic profiling of L. monocytogenes is valuable to track bacterial contamination throughout the FPE and in understanding persistence mechanisms, with limited studies from South Africa. Forty-six L. monocytogenes isolates from origins: Fish/seafood products (n = 32) (salmon, smoked trout, fresh hake, oysters), the FPE (n = 6), and clinical (n = 8) were included in this study. Lineage typing, antibiotic susceptibility testing, and screening for two genes (bcrABC and emrC) conferring sanitizer tolerance was conducted. The seafood and FPE isolates originated from seven different factories processing various seafood products with undetermined origin. All clinical isolates were categorized as lineage I, and seafood and FPE isolates were mostly categorized into lineage II (p < 0.01). Seafood and FPE isolates (53%) carried the bcrABC gene cassette and one fish isolate, the emrC gene. A subset, n = 24, was grouped into serotypes, sequence types (STs), and clonal complexes (CCs) with whole genome sequencing (WGS). Eight CCs and ten STs were identified. All clinical isolates belonged to serogroup 4b, hypervirulent CC1. CC121 was the most prevalent in isolates from food and the FPE. All isolates carried Listeria pathogenicity islands (LIPI) 1 and 2. LIPI-3 and LIPI-4 were found in certain isolates. We identified genetic determinants linked to enhanced survival in the FPE, including stress survival islets (SSI) and genes conferring tolerance to sanitizers. SSI-1 was found in 44% isolates from seafood and the FPE. SSI-2 was found in all the ST121 seafood isolates. Isolates (42%) harbored transposon Tn1688_qac (ermC), conferring tolerance to quaternary ammonium compounds. Five plasmids were identified in 13 isolates from seafood and the FPE. This is the first One Health study reporting on L. monocytogenes genetic diversity, virulence and resistance profiles from various types of seafood and its FPE in South Africa.

Distribution and genetic characterization of fluoroquinolone resistance gene qnr among Salmonella strains from chicken in China

The prevalence and dissemination of the plasmid-mediated fluoroquinolone (FQ) resistance gene qnr in Salmonella are considered serious public health concerns worldwide. So far, no comprehensive large-scale studies have focused on the prevalence and genetic characteristics of the qnr gene in Salmonella isolated from chickens. Herein, this study aimed to investigate the prevalence, antimicrobial resistance (AMR) patterns, and molecular characteristics of chicken-originated qnr-positive Salmonella strains from chicken farms, slaughterhouses, and markets in 12 provinces of China in 2020-2021. The overall prevalence of the qnr gene was 21.13% (56/265), with the highest prevalence in markets (36.11%, 26/72), followed in farms (17.95%, 21/117), and slaughterhouses (10.53%, 9/76). Only the qnrS and qnrB genes were detected, and the prevalence rate of the qnrS gene (19.25%, 51/265) was higher than that of the qnrB gene (1.89%, 5/265). Whole genome sequencing identified 37 distinct AMR genes and 15 plasmid replicons, and the most frequent mutation in quinolone resistance determining regions was parC (T57S; 91.49%, 43/47). Meanwhile, four different qnrS and two qnrB genetic environments were discovered among 47 qnr-positive Salmonella strains. In total, 21.28% (10/47) of the strains were capable of conjugative transfer, and all were qnrS1-positive strains, with the majority of transferable plasmids being IncHI2 types (n = 4). Overall, the prevalence of qnr-positive Salmonella strains from chickens in China and their carriage of multiple resistance and virulence genes and transferable plasmids is a major concern, which calls for continuous surveillance of qnr-positive Salmonella and the development of measures to control its prevalence and transmission.IMPORTANCESalmonella is a common foodborne pathogen responsible for 155,000 deaths annually worldwide. Fluoroquinolones (FQs) are used as first-line drugs for the treatment of Salmonella infections in several countries and regions. However, the emergence and increasing prevalence of the FQ-resistant gene qnr in Salmonella isolated from chickens have been widely reported. Gaining insight into the genetic mechanisms of AMR genes in chicken could lead to the development of preventive measures to control and reduce the risk of drug resistance. In this study, we identified qnr-positive Salmonellae isolated from chickens in different regions of China and their AMR patterns and genome-wide characteristics, providing a theoretical basis for further control of their prevalence and transmission.

Prevalence and Genomic Investigation of Salmonella Isolates Associated with Watermelons and Their Environmental Reservoirs in Bejaia, Algeria

This study was conducted in Bejaia, Algeria, to determine the presence of Salmonella in fresh watermelon (n = 105), soil (n = 23), and irrigation water samples (n = 17) collected from two different farms. After isolation, antimicrobial susceptibility testing, serotype determination, multilocus sequence typing, antimicrobial resistance genes detection, and whole genome sequencing were performed. Twenty watermelon samples (19%) were contaminated with Salmonella, but none were found in the soil or irrigation water. Among the 20 Salmonella isolates, 2 serovars were identified (Salmonella Liverpool and Salmonella Anatum), belonging to sequence types ST1959 and ST64, respectively. Ten Salmonella isolates showed significant resistance to nalidixic acid, ofloxacin, and ciprofloxacin but were susceptible to all other antibiotics. The coexistence of point mutations (parC:p.T57S) in Quinolone Resistance-Determining Regions and the qnrB19 gene may contribute to quinolone resistance. The study identified 164 virulence genes in the Salmonella isolates. Our study found Salmonella in fresh watermelon during the preharvest season in Bejaia, Algeria. Our study indicates a relatively high prevalence of Salmonella on watermelon samples before harvest. Although we cannot directly compare our results with previous studies, it is crucial to recognize that the absence of comprehensive comparative data underscores the need for further research and surveillance.

Genetic Characteristics of Salmonella Isolates Recovered From Reused Broiler Litter Over Three Successive Flocks

Salmonella infections are a leading cause of bacterial food-borne illness worldwide. Infections are highly associated with the consumption of contaminated food, and in particular, chicken meat. The severity of Salmonella infections depends on the presence of antimicrobial resistance genes and virulence factors. While there are many studies which have investigated Salmonella strains isolated from postharvest chicken samples, there is a gap in our understanding of the genetic properties that influence the persistence of Salmonella in preharvest and in particular their makeup of antimicrobial resistance genes and virulence factors. We used whole genome sequencing and hierarchical clustering to characterize and classify the genetic diversity of Salmonella enterica isolates (n = 55) recovered from the litter of commercial broiler chicken raised in four colocated broiler houses of one integrated farm over three consecutive flocks. The chicken were raised under a newly adopted "No Antibiotics Ever" program, and copper sulfate was administered via drinking water. In-silico serovar prediction identified three S. enterica serovars: Enteritidis (n = 12), Kentucky (n = 40), and Senftenberg (n = 3). Antimicrobial susceptibility testing revealed that only one S. Kentucky isolate was resistant to streptomycin, while the remaining isolates were susceptible to all antibiotics tested. Metal resistance operons, including copper and silver, were identified chromosomally and on plasmids in serovar Senftenberg and Kentucky isolates, respectively, while serovar Enteritidis carried several virulence factors on plasmids. Serovar Kentucky isolates harboring metal resistance operons were the only Salmonella isolates recovered from the litter of third flock cohort. These results suggest that there might be environmental selection for Salmonella strains carrying plasmid-associated metal resistance and virulence genes, which could play a role in their persistence in litter.

Genotyping of Campylobacter jejuni and prediction tools of its antimicrobial resistance

Although Campylobacter jejuni is the pathogen responsible for the most common foodborne illness, tracing of the infection source remains challenging due to its highly variable genome. Therefore, one of the aim of the study was to compare three genotyping methods (MLST, PFGE, and mP-BIT) to determine the most effective genotyping tool. C. jejuni strains were divided into 4 clusters based on strain similarity in the cgMLST dendrogram. Subsequently, the dendrograms of the 3 tested methods were compared to determine the accuracy of each method compared to the reference cgMLST method. Moreover, a cost-benefit analysis has showed that MLST had the highest inverse discrimination index (97%) and required less workflow, time, fewer consumables, and low bacterial sample quantity. PFGE was shown to be obsolete both because of its low discriminatory power and the complexity of the procedure. Similarly, mP‑BIT showed low separation results, which was compensated by its high availability. Therefore, our data showed that MLST is the optimal tool for genotyping C. jejuni. Another aim was to compare the antimicrobial resistance to ciprofloxacin, erythromycin, and tetracycline in C. jejuni strains isolated from human, water, air, food, and animal samples by two gene sequence-based prediction methods and to compare them with the actual susceptibility of C. jejuni strains using the disc diffusion method. Both tools, ResFinder and RGI, synchronously predict the antimicrobial susceptibility of C. jejuni and either can be used.

An investigation of the presence and antimicrobial susceptibility of Enterobacteriaceae in raw and cooked kibble diets for dogs in the United Kingdom

Raw meat diets (RMD) for dogs are an increasingly popular alternative pet food choice, however studies worldwide have demonstrated them to be contaminated with zoonotic and antimicrobial resistant (AMR) bacteria, including bacteria resistant to critically important antibiotics. Despite this, few data exist surrounding the presence of these bacteria in RMD in the United Kingdom. The present study aimed to identify the most commonly selected RMD and non-raw diets (NRMD) by United Kingdom dog owners. Additionally, it investigated the presence of AMR-Enterobacteriaceae in samples of pre-prepared RMD and cooked commercial kibble dog foods. An online survey investigating diet preferences of United Kingdom dog owners was open for 6 weeks between February-March 2020. From this, the top 10 brands of pre-prepared raw and cooked kibble diets were ascertained and 134 samples purchased (110 RMD, 24 kibble) and subjected to microbiological testing. Bacterial enumeration of E. coli and other Enterobacteriaceae was undertaken, and the presence of Salmonella spp. and AMR-E. coli within samples determined. Whole genome sequencing was undertaken on Salmonella spp. and third-generation cephalosporin-resistant 3GCR-E. coli isolates. Pre-prepared RMD was most commonly selected by dog owners who fed RMD, and cooked commercial complete dry food was most frequently fed by owners who fed NRMD. Damaged and leaking packaging was observed in samples of RMD, alongside variability in information provided surrounding product traceability. Counts of E. coli and other Enterobacteriaceae exceeding >5,000 CFU/g were identified in samples of RMD. AMR-, extended-spectrum beta-lactamase (ESBL)-producing and 3GCR-E. coli was isolated from 39, 14 and 16% of RMD samples, respectively. Multiple antimicrobial resistance genes were identified in 3GCR-E. coli isolates. Of the ESBL encoding genes, blaCTX-M-15 was most commonly identified. S. enterica was isolated from 5% of RMD samples. No Enterobacteriaceae were isolated from any of the cooked kibble samples. The present study suggests that pre-prepared RMD available for dogs in the United Kingdom can be contaminated with zoonotic and AMR-Enterobacteriaceae. RMDs, therefore, are potentially an important One Health concern. Veterinary and medical professionals, pet food retailers and pet owners should be aware of these risks; and stringent hygiene measures should be practiced if owners choose to feed RMD.

Analysis of Whole Genome Sequencing Data for Detection of Antimicrobial Resistance Determinants

Genomic sequencing has revolutionized microbial typing methods and transformed high-throughput methods in reference, clinical, and research laboratories. The detection of antimicrobial-resistant (AMR) determinants using genomic methods can provide valuable information on the emergence of resistance. Here we describe an approach to detecting AMR determinants using an open access and freely available platform which does not require bioinformatic expertise.

Genomic characterization of Salmonella isolated from retail chicken and humans with diarrhea in Qingdao, China

Salmonella, especially antimicrobial resistant strains, remains one of the leading causes of foodborne bacterial disease. Retail chicken is a major source of human salmonellosis. Here, we investigated the prevalence, antimicrobial resistance (AMR), and genomic characteristics of Salmonella in 88 out of 360 (24.4%) chilled chicken carcasses, together with 86 Salmonella from humans with diarrhea in Qingdao, China in 2020. The most common serotypes were Enteritidis and Typhimurium (including the serotype I 4,[5],12:i:-) among Salmonella from both chicken and humans. The sequence types were consistent with serotypes, with ST11, ST34 and ST19 the most dominantly identified. Resistance to nalidixic acid, ampicillin, tetracycline and chloramphenicol were the top four detected in Salmonella from both chicken and human sources. High multi-drug resistance (MDR) and resistance to third-generation cephalosporins resistance were found in Salmonella from chicken (53.4%) and humans (75.6%). In total, 149 of 174 (85.6%) Salmonella isolates could be categorized into 60 known SNP clusters, with 8 SNP clusters detected in both sources. Furthermore, high prevalence of plasmid replicons and prophages were observed among the studied isolates. A total of 79 antimicrobial resistant genes (ARGs) were found, with aac(6')-Iaa, blaTEM-1B, tet(A), aph(6)-Id, aph(3″)-Ib, sul2, floR and qnrS1 being the dominant ARGs. Moreover, nine CTX-M-type ESBL genes and the genes blaNMD-1, mcr-1.1, and mcr-9.1 were detected. The high incidence of MDR Salmonella, especially possessing lots of mobile genetic elements (MGEs) in this study posed a severe risk to food safety and public health, highlighting the importance of improving food hygiene measures to reduce the contamination and transmission of this bacterium. Overall, it is essential to continue monitoring the Salmonella serotypes, implement the necessary prevention and strategic control plans, and conduct an epidemiological surveillance system based on whole-genome sequencing.

Genomics for public health and international surveillance of antimicrobial resistance

Historically, epidemiological investigation and surveillance for bacterial antimicrobial resistance (AMR) has relied on low-resolution isolate-based phenotypic analyses undertaken at local and national reference laboratories. Genomic sequencing has the potential to provide a far more high-resolution picture of AMR evolution and transmission, and is already beginning to revolutionise how public health surveillance networks monitor and tackle bacterial AMR. However, the routine integration of genomics in surveillance pipelines still has considerable barriers to overcome. In 2022, a workshop series and online consultation brought together international experts in AMR and pathogen genomics to assess the status of genomic applications for AMR surveillance in a range of settings. Here we focus on discussions around the use of genomics for public health and international AMR surveillance, noting the potential advantages of, and barriers to, implementation, and proposing recommendations from the working group to help to drive the adoption of genomics in public health AMR surveillance. These recommendations include the need to build capacity for genome sequencing and analysis, harmonising and standardising surveillance systems, developing equitable data sharing and governance frameworks, and strengthening interactions and relationships among stakeholders at multiple levels.

Characterization of Salmonella enterica serovar Isangi from South Africa, 2020-2021

BACKGROUND

We describe the genotypic characteristics and antimicrobial resistance (AMR) determinants of Salmonella enterica serovar Isangi (Salmonella Isangi) clinical isolates in South Africa from 2020 through 2021.

METHODS

During the years 2020 to 2021, the Centre for Enteric Diseases of the National Institute for Communicable Diseases, a national reference centre in South Africa for human infections resulting from enteric bacterial pathogens, investigated a total of 3549 clinical isolates of Salmonella species. Whole genome sequencing (WGS) was performed using Illumina NextSeq Technology. WGS data was analyzed using Centre for Genomic Epidemiology-based tools and EnteroBase web-based platform. Genotypic relatedness and cluster analysis was investigated based on core-genome multilocus sequence typing.

RESULTS

Forty-nine isolates were confirmed to be Salmonella Isangi, with most submitted from Gauteng Province (24/49, 49%). The most prevalent sequence type was ST335 (48/49, 98%), and the remaining 1 isolate was ST216. All ST335 isolates were genotypically multidrug-resistant (MDR), with resistance to fluoroquinolones, chloramphenicol, trimethoprim-sulfamethoxazole and tetracycline; the ST216 isolate was resistant only to aminoglycosides. All ST335 isolates carried ESBL genes, the most common being blaCTX-M-15. Five clusters (consisting of isolates related within five allele differences) were detected, all being ST335.

CONCLUSIONS

Most Salmonella Isangi isolates in South Africa are MDR and ESBL-positive. Ongoing monitoring of the epidemiology and AMR profile of this serovar is important for public health and treatment guidelines.

Genetic diversity of Salmonella enterica isolated over 13 years from raw California almonds and from an almond orchard

A comparative genomic analysis was conducted for 171 Salmonella isolates recovered from raw inshell almonds and raw almond kernels between 2001 and 2013 and for 30 Salmonella Enteritidis phage type (PT) 30 isolates recovered between 2001 and 2006 from a 2001 salmonellosis outbreak-associated almond orchard. Whole genome sequencing was used to measure the genetic distance among isolates by single nucleotide polymorphism (SNP) analyses and to predict the presence of plasmid DNA and of antimicrobial resistance (AMR) and virulence genes. Isolates were classified by serovars with Parsnp, a fast core-genome multi aligner, before being analyzed with the CFSAN SNP Pipeline (U.S. Food and Drug Administration Center for Food Safety and Applied Nutrition). Genetically similar (≤18 SNPs) Salmonella isolates were identified among several serovars isolated years apart. Almond isolates of Salmonella Montevideo (2001 to 2013) and Salmonella Newport (2003 to 2010) differed by ≤9 SNPs. Salmonella Enteritidis PT 30 isolated between 2001 and 2013 from survey, orchard, outbreak, and clinical samples differed by ≤18 SNPs. One to seven plasmids were found in 106 (62%) of the Salmonella isolates. Of the 27 plasmid families that were identified, IncFII and IncFIB plasmids were the most predominant. AMR genes were identified in 16 (9%) of the survey isolates and were plasmid encoded in 11 of 16 cases; 12 isolates (7%) had putative resistance to at least one antibiotic in three or more drug classes. A total of 303 virulence genes were detected among the assembled genomes; a plasmid that harbored a combination of pef, rck, and spv virulence genes was identified in 23% of the isolates. These data provide evidence of long-term survival (years) of Salmonella in agricultural environments.

The genomic approach of antimicrobial resistance of Salmonella Typhimurium isolates from guinea pigs in Lima, Peru

Salmonella Typhimurium is an important agent of foodborne diseases. In Peru, the emergence of multidrug-resistant isolates of S. Typhimurium from the food chain could be linked to guinea pig farming as a potential reservoir and their uncontrolled antibiotic treatment against salmonellosis. In this study, we performed the sequencing, genomic diversity, and characterization of resistance elements transmitted by isolates from farm and meat guinea pigs. The genomic diversity and antimicrobial resistance of S. Typhimurium isolates were performed using nucleotide similarity, cgMLST, serotyping, phylogenomic analyses, and characterization of resistance plasmids. We found at least four populations of isolates from farm guinea pigs and four populations from meat guinea pigs without finding isolated transmission between both resources. Genotypic resistance to antibiotics was observed in at least 50% of the isolates. Among the farm guinea pig isolates, ten were found to be resistant to nalidixic acid, and two isolates exhibited multidrug resistance to aminoglycosides, tetracycline-fluoroquinolone (carrying strA-strB-tetA-tetB genes and gyrA S83F mutation), or trimethoprim-sulfonamide (carrying AaadA1-drfA15-sul1 genes). Additionally, two isolates from the meat source were resistant to fluoroquinolones (one of which had enrofloxacin resistance). The transmissible resistance plasmids with insertion sequences (IS) such as IncI-gamma-K1-ISE3-IS6, IncI1-I (alpha)-IS21-Tn10, and Col (pHAD28) were commonly found in isolates belonging to the HC100-9757 cluster from both guinea pigs and human hosts. Altogether, our work provides resistance determinants profiles and Salmonella sp. circulating lineages using WGS data that can promote better sanitary control and adequate antimicrobial prescription.

Serotyping and Antimicrobial Resistance Profiling of Multidrug-Resistant Non-Typhoidal Salmonella from Farm Animals in Hunan, China

Non-typhoidal Salmonella (NTS) is a foodborne pathogen and a prevalent causative agent for disease outbreaks globally. The Salmonella enterica serovar 4,[5],12:i:- (S.4,[5],12:i:-) belongs to the monophasic variant of Salmonella typhimurium, which is of current global concern. In this study, the epidemiology and genomic characterization of S. 4,[5],12:i:- isolates from 17 livestock farms in Hunan Province between 2019 and 2020, as well as their susceptibility to 14 antimicrobial agents, were profiled. Twelve Salmonella serotypes were identified using the White-Kauffmann-Le Minor scheme, and whole-genome sequencing analyses were conducted based on these isolates. Overall, 107 Salmonella strains were isolated, of which 73% (78/107) were multidrug resistant. Resistance to tetracycline (85.05%) was found to be the most prevalent, followed by the oqxAB and aac(6')-Ib-cr genes. S. typhimurium (monophasic) 4,[5],12:i:- was the most common serotype, followed by S. typhimurium and S. derby. Most antimicrobial-resistant strains were isolated from pigs, indicating that they could be important reservoirs of resistant non-typhoidal Salmonella strains. The presence of similar genetic environments in S. 4,[5],12:i:- indicates both vertical and horizontal transmission of resistance plasmids, which may promote the spread of drug resistance genes. Appropriate measures should be taken to curb the prevalence of S. 4,[5],12:i:-.

Is it time to move on to gene-based Salmonella typing: Evidence and implications

Non-typhoidal Salmonella (NTS) is the major cause of foodborne infections globally, with considerable morbidity and mortality. The accurate identification of Salmonella serovars is important in disease management and public health surveillance. However, traditional serotyping methods are laborious, time-consuming and may produce ambiguous results. In this study, we evaluated traditional serotyping and seven gene-based multilocus sequence typing (MLST) methods to determine the serogroups of Salmonella strains. This study analysis suggests that MLST based serotyping is accurate in serogroup identification and discrimination of Salmonella serovars compared to the traditional serotyping method and can be implemented in routine clinical practice.

Investigation of multidrug-resistant plasmids from carbapenemase-producing Klebsiella pneumoniae clinical isolates from Pakistan

Objectives

The study aim was to investigate multidrug-resistant (MDR) plasmids from a collection of 10 carbapenemase-producing Klebsiella pneumoniae clinical isolates identified within the same healthcare institution in Pakistan. Full characterization of the MDR plasmids including structure, typing characteristics, and AMR content as well as determination of their plasmid-based antimicrobial susceptibility profiles were carried out.

Methods

Plasmids were isolated from 10 clinical isolates of Klebsiella pneumoniae, and from a corresponding set of Escherichia coli transconjugants, then sequenced using Nanopore/Illumina technology to generate plasmid hybrid assemblies. Full characterization of MDR plasmids, including determination of next generation sequencing (NGS)-based AMR profiles, plasmid incompatibility groups, and types, was carried out. The structure of MDR plasmids was analyzed using the Galileo AMR platform. For E. coli transconjugants, the NGS-based AMR profiles were compared to NGS-predicted AMR phenotypes and conventional broth microdilution (BMD) antimicrobial susceptibility testing (AST) results.

Results

All carbapenemase-producing K. pneumoniae isolates (carrying either blaNDM-1, or/and blaOXA-48) carried multiple AMR plasmids encoding 34 antimicrobial resistance genes (ARGs) conferring resistance to antimicrobials from 6 different classes. The plasmid incompatibility groups and types identified were: IncC (types 1 and 3), IncFIA (type 26) IncFIB, IncFII (types K1, K2, K7, and K9), IncHI1B, and IncL. None of the blaNDM-1 and blaESBL-plasmids identified in this study were previously described. Most blaNDM-1-plasmids shared identical AMR regions suggesting potential genetic material/plasmid exchange between K. pneumoniae isolates of this collection. The majority of NGS-based AMR profiles from the E. coli transconjugants correlated well with both NGS-based predicted and conventional AST results.

Conclusion

This study highlights the complexity and diversity of the plasmid-based genetic background of carbapenemase-producing clinical isolates from Pakistan. This study emphasizes the need for characterization of MDR plasmids to determine their complete molecular background and monitor AMR through plasmid transmission between multi-resistant bacterial pathogens.

Salmonella Typhi whole genome sequencing in Rwanda shows a diverse historical population with recent introduction of haplotype H58

Salmonella enterica serovar Typhi (S. Typhi) is the cause of typhoid fever, presenting high rates of morbidity and mortality in low- and middle-income countries. The H58 haplotype shows high levels of antimicrobial resistance (AMR) and is the dominant S. Typhi haplotype in endemic areas of Asia and East sub-Saharan Africa. The situation in Rwanda is currently unknown and therefore to reveal the genetic diversity and AMR of S. Typhi in Rwanda, 25 historical (1984-1985) and 26 recent (2010-2018) isolates from Rwanda were analysed using whole genome sequencing (WGS). WGS was locally implemented using Illumina MiniSeq and web-based analysis tools, thereafter complemented with bioinformatic approaches for more in-depth analyses. Whereas historical S. Typhi isolates were found to be fully susceptible to antimicrobials and show a diversity of genotypes, i.e 2.2.2, 2.5, 3.3.1 and 4.1; the recent isolates showed high AMR rates and were predominantly associated with genotype 4.3.1.2 (H58, 22/26; 84,6%), possibly resulting from a single introduction in Rwanda from South Asia before 2010. We identified practical challenges for the use of WGS in endemic regions, including a high cost for shipment of molecular reagents and lack of high-end computational infrastructure for the analyses, but also identified WGS to be feasible in the studied setting and giving opportunity for synergy with other programs.

Graphical abstractGenotypic and Phenotypic Characterization of Antimicrobial and Heavy Metal tolerance in Salmonella enterica and Escherichia coli Isolates from Swine Feed Mills

Antimicrobials and heavy metals are commonly used in the animal feed industry. The role of in-feed antimicrobials on the evolution and persistence of resistance in enteric bacteria is not well described. Whole-Genome Sequencing (WGS) is widely used for genetic characterizations of bacterial isolates, including antimicrobial resistance, heavy metal tolerance, virulence factors, and relatedness to other sequenced isolates. The goals of this study were to i) use WGS to characterize Salmonella enterica (n = 33) and Escherichia coli (n = 30) isolated from swine feed and feed mill environments; and ii) investigate their genotypic and phenotypic antimicrobial and heavy metal tolerance. Salmonella isolates belonged to 10 serovars, the most common being Cubana, Senftenberg, and Tennessee. E. coli isolates were grouped into 22 O groups. Phenotypic resistance to at least one antimicrobial was observed in 19 Salmonella (57.6%) and 17 E. coli (56.7%) isolates, whereas multidrug resistance (resistant to ≥ 3 antimicrobial classes) was observed in four Salmonella (12%) and two E. coli (7%) isolates. Antimicrobial resistance genes were identified in 17 Salmonella (51%) and 29 E. coli (97%), with 11 and 29 isolates possessing genes conferring resistance to multiple antimicrobial classes. Phenotypically, 53% Salmonella and 58% E. coli presented resistance to copper and arsenic. All isolates that possessed the copper resistance operon were resistant to the highest concentration tested (40 mM). Heavy metal tolerance genes to copper and silver were present in 26 Salmonella isolates. Our study showed a strong agreement between predicted and measured resistances when comparing genotypic and phenotypic data for antimicrobial resistance, with an overall concordance of 99% and 98.3% for Salmonella and E. coli, respectively.

Oxford nanopore technologies-a valuable tool to generate whole-genome sequencing data for in silico serotyping and the detection of genetic markers in Salmonella

Bacteria of the genus Salmonella pose a major risk to livestock, the food economy, and public health. Salmonella infections are one of the leading causes of food poisoning. The identification of serovars of Salmonella achieved by their diverse surface antigens is essential to gain information on their epidemiological context. Traditionally, slide agglutination has been used for serotyping. In recent years, whole-genome sequencing (WGS) followed by in silico serotyping has been established as an alternative method for serotyping and the detection of genetic markers for Salmonella. Until now, WGS data generated with Illumina sequencing are used to validate in silico serotyping methods. Oxford Nanopore Technologies (ONT) opens the possibility to sequence ultra-long reads and has frequently been used for bacterial sequencing. In this study, ONT sequencing data of 28 Salmonella strains of different serovars with epidemiological relevance in humans, food, and animals were taken to investigate the performance of the in silico serotyping tools SISTR and SeqSero2 compared to traditional slide agglutination tests. Moreover, the detection of genetic markers for resistance against antimicrobial agents, virulence, and plasmids was studied by comparing WGS data based on ONT with WGS data based on Illumina. Based on the ONT data from flow cell version R9.4.1, in silico serotyping achieved an accuracy of 96.4 and 92% for the tools SISTR and SeqSero2, respectively. Highly similar sets of genetic markers comparing both sequencing technologies were identified. Taking the ongoing improvement of basecalling and flow cells into account, ONT data can be used for Salmonella in silico serotyping and genetic marker detection.

Advantages of Whole Genome Sequencing in Mitigating the Helicobacter pylori Antimicrobial Resistance Problem

Helicobacter pylori antimicrobial resistance is a critical public health issue. Typically, antimicrobial resistance epidemiology reports include only the antimicrobial susceptibility test results for H. pylori. However, this phenotypic approach is less capable of answering queries related to resistance mechanisms and specific mutations found in particular global regions. Whole genome sequencing can help address these two questions while still offering quality control and is routinely validated against AST standards. A comprehensive understanding of the mechanisms of resistance should improve H. pylori eradication efforts and prevent gastric cancer.

Assessment of Prevalence and Diversity of Antimicrobial Resistant Escherichia coli from Retail Meats in Southern California

Retail meat products may serve as reservoirs and conduits for antimicrobial resistance, which is frequently monitored using Escherichia coli as indicator bacteria. In this study, E. coli isolation was conducted on 221 retail meat samples (56 chicken, 54 ground turkey, 55 ground beef, and 56 pork chops) collected over a one-year period from grocery stores in southern California. The overall prevalence of E. coli in retail meat samples was 47.51% (105/221), with E. coli contamination found to be significantly associated with meat type and season of sampling. From antimicrobial susceptibility testing, 51 isolates (48.57%) were susceptible to all antimicrobials tested, 54 (51.34%) were resistant to at least 1 drug, 39 (37.14%) to 2 or more drugs, and 21 (20.00%) to 3 or more drugs. Resistance to ampicillin, gentamicin, streptomycin, and tetracycline were significantly associated with meat type, with poultry counterparts (chicken or ground turkey) exhibiting higher odds for resistance to these drugs compared to non-poultry meats (beef and pork). From the 52 E. coli isolates selected to undergo whole-genome sequencing (WGS), 27 antimicrobial resistance genes (ARGs) were identified and predicted phenotypic AMR profiles with an overall sensitivity and specificity of 93.33% and 99.84%, respectively. Clustering assessment and co-occurrence networks revealed that the genomic AMR determinants of E. coli from retail meat were highly heterogeneous, with a sparsity of shared gene networks.

Salmonella Heidelberg and Salmonella Minnesota in Brazilian broilers: Genomic characterization of third-generation cephalosporin and fluoroquinolone-resistant strains

Salmonella serovars Heidelberg and Minnesota encoding antimicrobial resistance to third-generation cephalosporins and fluoroquinolones are often detected in poultry/poultry meat. We analysed the genomes of 10 Salmonella Heidelberg (SH) and 4 Salmonella Minnesota (SM) from faecal isolates of Brazilian poultry. These featured virulent and multidrug-resistant characteristics, with AmpC beta-lactamase (bla_CMY-2 ) predominance (9/14), for all SM (4/4) and some SH (3/10) located on IncC plasmid replicons. IncC carrying bla_CTX-M-2 was only detected among SH (3/10). Mutation in the gyrA/parC genes was present in all SH, whereas SM harboured parC mutation plus qnrB19 on ColRNAI plasmids (3/4). In silico resistance overall corroborated with phenotypic results. Core genome phylogenies showed close clustering and high similarities between the Brazilian and poultry meat/food isolates from Europe, and to human isolates from European countries with documented import of Brazilian poultry meat. Conjugation assays with SM successfully transferred bla_CMY-2 , and qnrB19 to an Escherichia coli recipient. The findings reinforce the ongoing antimicrobial resistance acquisition of SH and Minnesota and the risks for disseminating resistant strains and/or mobile elements which may increasingly affect importing countries and the need for controlling AMR in major poultry-exporting countries like Brazil.

Phenotypic and genotypic survey of antibiotic resistance in Salmonella enterica isolates from dairy farms in Uruguay

Salmonella enterica is an important zoonotic pathogen that is frequently identified in dairy farming systems. An increase in antibiotic resistance has led to inadequate results of treatments, with impacts on animal and human health. Here, the phenotypic and genotypic susceptibility patterns of Salmonella isolates from dairy cattle and dairy farm environments were evaluated and compared. A collection of 75 S. enterica isolates were evaluated, and their phenotypic susceptibility was determined. For genotypic characterization, the whole genomes of the isolates were sequenced, and geno-serotypes, sequence types (STs) and core-genome-sequence types were determined using the EnteroBase pipeline. To characterize antibiotic resistance genes and gene mutations, tools from the Center for Genomic Epidemiology were used. Salmonella Dublin (SDu), S. Typhimurium (STy), S. Anatum (SAn), S. Newport (SNe), S. Agona (Sag), S. Montevideo (SMo) and IIIb 61:i:z53 were included in the collection. A single sequence type was detected per serovar. Phenotypic non-susceptibility to streptomycin and tetracycline was very frequent in the collection, and high non-susceptibility to ciprofloxacin was also observed. Multidrug resistance (MDR) was observed in 42 isolates (56.0%), with SAn and STy presenting higher MDR than the other serovars, showing non-susceptibility to up to 6 groups of antibiotics. Genomic analysis revealed the presence of 21 genes associated with antimicrobial resistance (AMR) in Salmonella isolates. More than 60% of the isolates carried some gene associated with resistance to aminoglycosides and tetracyclines. Only one gene associated with beta-lactam resistance was found, in seven isolates. Two different mutations were identified, parC_T57S and acrB_R717Q, which confer resistance to quinolones and azithromycin, respectively. The accuracy of predicting antimicrobial resistance phenotypes based on AMR genotypes was 83.7%. The genomic approach does not replace the phenotypic assay but offers valuable information for the survey of circulating antimicrobial resistance. This work represents one of the first studies evaluating phenotypic and genotypic AMR in Salmonella from dairy cattle in South America.

The temporal dynamics of antimicrobial-resistant Salmonella enterica and predominant serovars in China

Salmonella enterica is one of the most common bacterial pathogens in humans and animals. Systematic studies on the trends and geographical distribution of antimicrobial-resistant Salmonella and dominant serovars have been well studied in European and American countries while not in China. Here, taking the One-Health strategy, we used >35 000 Salmonella enterica isolates to explore the temporal and spatial dynamics of dominant serovars in China. We found that Salmonella Typhimurium was the dominant serovar causing human infection in China, which was consistent with Australia but inconsistent with North American and European countries. The proportion of Salmonella serovars Typhimurium, London, Rissen, Corvallis, Meleagridis, Kentucky, and Goldcoast showed an increasing trend during 2006-2019. We randomly selected 1962 isolates for comparative genomics and antimicrobial resistance studies and found that the number of antibiotic resistance genes (ARGs) per isolate increased 1.84 and 2.69 times of human and non-human origins, respectively, spanning 14 years. The proportion of antimicrobial-resistant Salmonella isolates had an increasing trend during 2006-2019, especially beta-lactam, quinolone, tetracycline, and rifampicin resistance. Moreover, we found that higher diversity of sequence types (STs) in S. Typhimurium than in other serovars, ST34 from pig and ST19 from chicken origin, were mainly associated with isolates causing child and adult gastro-infection, respectively. Our results fill in the data gap on the trends of dominant serovars and antimicrobial resistance of Salmonella enterica in China. These data provide useful information for public health decision-makers prioritizing interventions for foodborne diseases and food safety.

Prevalence and resistance to antibacterial agents in Salmonella enterica strains isolated from poultry products in Northern Kazakhstan

Background and Aim: Salmonella is one of the main causative agents of foodborne infections. The source of the pathogen, in most cases, is poultry products. The intensification of poultry farming and the constant and uncontrolled use of antimicrobials has led to an increase in the level of antibiotic resistance, especially in developing countries. This study aimed to determine the level of sensitivity to antimicrobial agents in Salmonella enterica strains isolated from poultry products in Northern Kazakhstan, as well as to determine the genetic mechanisms of resistance and the presence of integrons. Materials and Methods: In total, 398 samples of poultry products sold in Northern Kazakhstan were selected. Salmonella strains were isolated from product samples using microbiological methods. Salmonella was identified based on morphological, biochemical, and serological methods, as well as polymerase chain reaction (PCR). Sensitivity testing for antimicrobial agents was performed using the disk diffusion method. The detection of resistance genes was performed using PCR and gel electrophoresis. Results: Out of 398 samples of poultry products, a total of 46 Salmonella isolates were obtained. Most of the isolates belong to the serovar Salmonella Enteritidis (80.4%). The assessment of sensitivity to antibacterial agents showed that Salmonella was mainly resistant to nalidixic acid (63%), furadonin (60.9%), ofloxacin (45.6%), and tetracycline (39.1%). In 64.3% of cases, Salmonella was resistant to three or more groups of antibacterial agents. Resistance genes such as tetA, tetB, blaTEM, aadA, sul3, and catII, as well as integrons of two classes (teg1 and teg2), were identified. Conclusion: Poultry products contain antimicrobial-resistant strains of Salmonella, as well as genes encoding resistance mechanisms. The results emphasize the need for constant monitoring of not only pathogenic microorganisms but also their sensitivity to antimicrobial agents. The potential threat to human health requires a unified approach to the problem of antibiotic resistance from representatives of both public health and the agroindustrial complex. Keywords: antibiotic resistance, food safety, poultry, resistance genes, Salmonella.

Evaluating the impact of heavy metals on antimicrobial resistance in the primary food production environment: A scoping review

Heavy metals are naturally occurring environmental compounds, which can influence antimicrobial resistance (AMR) dissemination. However, there is limited information on how heavy metals may act as a selective pressure on AMR in the primary food production environment. This review aims to examine the literature on this topic in order to identify knowledge gaps. A total of 73 studies, which met pre-established criteria, were included. These investigations were undertaken between 2008 and 2021, with a significant increase in the last three years. The majority of studies included were undertaken in China. Soil, water and manure were the most common samples analysed, and the sampling locations varied from areas with a natural presence of heavy metals, areas intentionally amended with heavy metals or manure, to areas close to industrial activity or mines. Fifty-four per cent of the investigations focused on the analysis of four or more heavy metals, and copper and zinc were the metals most frequently analysed (n = 59, n = 49, respectively). The findings of this review highlight a link between heavy metals and AMR in the primary food production environment. Heavy metals impacted the abundance and dissemination of mobile genetic elements (MGEs) and antimicrobial resistance genes (ARGs), with MGEs also observed as playing a key role in the spread of ARGs and metal resistance genes (MRGs). Harmonization of methodologies used in future studies would increase the opportunity for comparison between studies. Further research is also required to broaden the availability of data at a global level.

Comparative Analysis between Salmonella enterica Isolated from Imported and Chinese Native Chicken Breeds

Salmonella enterica is considered a significant threat to the global poultry industry and public health. In recent decades, antimicrobial resistance in Salmonella enterica has attracted increasing concern throughout the world. However, limited information is available on Salmonella enterica among different breeds of breeder chickens. Thus, this study aimed to compare the prevalence, serotype distribution, emergence of extended-spectrum beta-lactamases (ESBLs), antimicrobial resistance, and genetic resistance mechanisms in Salmonella enterica among different breeds of breeder chickens. A total of 693 samples (dead embryos, cloacal swabs, water, feed, environmental swabs, and meconium of newly hatched chicks) were selected and cultured for Salmonella from four breeder chicken farms in Shandong province, China, representing one imported and three native breeds, and the isolates were further serotyped. Of the Salmonella isolates, susceptibility to 11 antimicrobials of 5 classes, ESBL screening, and the presence of 21 antimicrobial resistance genes were determined in the present study. Overall, 94 (13.6%) isolates were recovered, which were divided into 3 serotypes (Salmonella Pullorum (n = 36), Salmonella Thompson (n = 32), and Salmonella Enteritidis (n = 26)). The results showed that the prevalence of Salmonella enterica isolates from the imported breeds was higher compared with the three domestic breeds. Eight of the ninety-four isolates were ESBL-positive strains, which were recovered from a domestic breed chicken farm. These eight ESBL-producing isolates were serotyped to Pullorum. Surprisingly, Salmonella Enteritidis (S. enteritidis) and S. pullorum were simultaneously isolated from a single dead embryo observed among one native breed. Meanwhile, among the Salmonella isolates, 53.2% (50/94) were multidrug-resistant strains, and 44.7% (42/94) of the isolates presented resistance to at least five antibiotics. Nearly all of the isolates (97.9%, 92/94) were resistant to at least one antimicrobial; one isolate of S. Thompson was resistant to seven antimicrobial agents belonging to four different classes. The carriage rate of three resistance genes (tetA, tetB, and sul1) among isolates from the imported breeds (87%, 70%, and 65.2%) was higher than that in those from domestic breeds (35.2%, 36.6, and 14.1%). To our knowledge, this is the first report of ESBLs-producing Salmonella isolated from a Chinese native breed of breeder chickens. Our results also highlight that a high prevalence of multidrug-resistant Salmonella enterica contamination is widespread among different breeds of breeder chickens, which is a major risk of food-borne diseases and public health.

Ecology and Evolutionary Biology of Hindering Phage Therapy: The Phage Tolerance vs. Phage Resistance of Bacterial Biofilms

As with antibiotics, we can differentiate various acquired mechanisms of bacteria-mediated inhibition of the action of bacterial viruses (phages or bacteriophages) into ones of tolerance vs. resistance. These also, respectively, may be distinguished as physiological insensitivities (or protections) vs. resistance mutations, phenotypic resistance vs. genotypic resistance, temporary vs. more permanent mechanisms, and ecologically vs. also near-term evolutionarily motivated functions. These phenomena can result from multiple distinct molecular mechanisms, many of which for bacterial tolerance of phages are associated with bacterial biofilms (as is also the case for the bacterial tolerance of antibiotics). The resulting inhibitions are relevant from an applied perspective because of their potential to thwart phage-based treatments of bacterial infections, i.e., phage therapies, as well as their potential to interfere more generally with approaches to the phage-based biological control of bacterial biofilms. In other words, given the generally low toxicity of properly chosen therapeutic phages, it is a combination of phage tolerance and phage resistance, as displayed by targeted bacteria, that seems to represent the greatest impediments to phage therapy's success. Here I explore general concepts of bacterial tolerance of vs. bacterial resistance to phages, particularly as they may be considered in association with bacterial biofilms.

A Glimpse at the Anti-Phage Defenses Landscape in the Foodborne Pathogen Salmonella enterica subsp. enterica serovar Typhimurium

Bacteriophages, which specifically infect and kill bacteria, are currently used as additives to control pathogens such as Salmonella in human food (PhageGuard S^®) or animal feed (SalmoFREE^®, Bafasal^®). Indeed, salmonellosis is among the most important zoonotic foodborne illnesses. The presence of anti-phage defenses protecting bacteria against phage infection could impair phage applications aiming at reducing the burden of foodborne pathogens such as Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) to the food industry. In this study, the landscape of S. Typhimurium anti-phage defenses was bioinformatically investigated in publicly available genomes using the webserver PADLOC. The primary anti-phage systems identified in S. Typhimurium use nucleic acid degradation and abortive infection mechanisms. Reference systems were identified on an integrative and conjugative element, a transposon, a putative integrative and mobilizable element, and prophages. Additionally, the mobile genetic elements (MGEs) containing a subset of anti-phage systems were found in the Salmonella enterica species. Lastly, the MGEs alone were also identified in the Enterobacteriaceae family. The presented diversity assessment of the anti-phage defenses and investigation of their dissemination through MGEs in S. Typhimurium constitute a first step towards the design of preventive measures against the spread of phage resistance that may hinder phage applications.

Antimicrobial resistance and genomic characterization of Salmonella enterica isolates from chicken meat

This study investigated genotypic and phenotypic antimicrobial resistance profiles, phylogenic relatedness, plasmid and virulence composition of 39 Salmonella enterica strains isolated from chicken meat samples using whole genome sequencing (WGS) technology. Four distinct serotypes were identified; Salmonella Minnesota (16/39, 41%), Salmonella Infantis (13/39, 33.3%), Salmonella Enteritidis (9/39, 23.1%), and one isolate was detected for Salmonella Kentucky (1/39, 2.6%), with sequence types (STs) as followed: ST548, ST32, ST11, and ST198, respectively. Phenotypic resistance to tetracycline (91.2%), ampicillin (82.4%), sulfisoxazole (64.7%), and nalidixic acid (61.6%) was the most observed. Resistome analysis revealed the presence of resistance genes to aminoglycosides, β-lactamase, sulfonamides, trimethoprim, phenicol, lincosamide, macrolides, and tetracyclines. Plasmidome showed the presence of eight incompatibility groups, including IncA/C2, IncFIB(K)_1_Kpn3, Col440I_1, IncR, IncX1, IncI1_1_Alpha, IncFIB(S)/IncFII(S), IncHI2/IncHI2A, IncX2 and ColpVC plasmids across the 39 genomes. Three resistance genes, sul2, tetA and bla_CMY-2, were predicted to be located on IncA/C2 plasmid in S. Minnesota isolates, whereas all S. Infantis isolates were positive to IncFIB(K)_1_Kpn3 plasmid that carries bla _CTX-M-65 gene. Eleven Salmonella pathogenicity islands and up to 131 stress and/or virulence genes were identified in the evaluated genomes. Phylogenetic analysis showed four phylogroups that were consistent with the identified ST profiles with a high level of inter-diversity between isolates. This is the first genomic characterization of Salmonella isolates from retail chicken meat in Saudi Arabia using WGS technology. The availability of Salmonella genomes from multiple geographic locations, including Saudi Arabia, would be highly beneficial in future source-tracking, especially during epidemiological surveillance and outbreak investigations.

Non-Typhoidal Salmonella Infections Among Children in Fuzhou, Fujian, China: A 10-Year Retrospective Review from 2012 to 2021

Purpose

Non-typhoidal salmonella (NTS) infection is a leading cause of acute gastroenteritis in children. Recently, NTS infections have increased, especially those associated with Salmonella Typhimurium, which has become a global problem because of its high level of drug resistance. Diseases caused by NTS serotypes vary considerably. We summarised NTS infections among children in Fuzhou, Fujian, China, from 2012 to 2021, and synthesised studies indicating the clinical symptoms, laboratory test results, and drug resistance associated with S. Typhimurium and non-S. Typhimurium to enhance the knowledge of these infections and improve their diagnoses and treatment.

Patients and Methods

Between January 2012 and December 2021, 691 children with NTS infections confirmed by positive culture test results were recruited from Fujian Children's Hospital and Fujian Maternity and Child Health Hospital. Clinical demographic data of each case were collected from the electronic medical records and analysed.

Results

A total of 691 isolates were identified. The number of NTS infections increased significantly in 2017 and increased sharply during 2020 and 2021, especially S. Typhimurium greatly increased and was the dominant serotype (58.3%). S. Typhimurium infection was commonly occurred in children younger than 3 years and most of them were gastrointestinal infection, while non-S. Typhimurium more often observed in older children and associated with extra-intestinal infection. The rate of multidrug-resistant S. Typhimurium was significantly higher than that of non-S. Typhimurium, especially during the last 2 years of this study (2020 and 2021).

Conclusion

S. Typhimurium was the dominant serotype and greatly increased among children in Fuzhou city. There are significant differences in clinical symptoms, laboratory test results, and drug resistance between S. Typhimurium and non-S. Typhimurium. More attention should be paid on S. Typhimurium. Long-term high-quality surveillance and control measures should be conducted to prevent salmonella infections and drug resistance.

Potential of Aromatic Plant-Derived Essential Oils for the Control of Foodborne Bacteria and Antibiotic Resistance in Animal Production: A Review

Antibiotic resistance has become a severe public threat to human health worldwide. Supplementing antibiotic growth promoters (AGPs) at subtherapeutic levels has been a commonly applied method to improve the production performance of livestock and poultry, but the misuse of antibiotics in animal production plays a major role in the antibiotic resistance crisis and foodborne disease outbreaks. The addition of AGPs to improve production performance in livestock and poultry has been prohibited in some countries, including Europe, the United States and China. Moreover, cross-resistance could result in the development of multidrug resistant bacteria and limit therapeutic options for human and animal health. Therefore, finding alternatives to antibiotics to maintain the efficiency of livestock production and reduce the risk of foodborne disease outbreaks is beneficial to human health and the sustainable development of animal husbandry. Essential oils (EOs) and their individual compounds derived from aromatic plants are becoming increasingly popular as potential antibiotic alternatives for animal production based on their antibacterial properties. This paper reviews recent studies in the application of EOs in animal production for the control of foodborne pathogens, summarizes their molecular modes of action to increase the susceptibility of antibiotic-resistant bacteria, and provides a promising role for the application of nanoencapsulated EOs in animal production to control bacteria and overcome antibiotic resistance.

Characterization of antibiotic-resistance traits in Akkermansia muciniphila strains of human origin

Akkermansia muciniphila, a commensal bacterium commonly found in healthy gut microbiota, is widely considered a next-generation beneficial bacterium candidate to improve metabolic and inflammatory disorders. Recently the EFSA's Panel on Nutrition, Novel food, and Food Allergens has declared that pasteurized A. muciniphila DSM 22959^T (also Muc^T, ATCC BAA-835) can be considered safe as a novel food, opening the door to its commercialization as a food supplement. Despite its recognized health benefits, there is still little information regarding the antimicrobial susceptibility of this species and reference cut-off values to distinguish strains with intrinsic or acquired resistance from susceptible strains. In this study, we combined a genomic approach with the evaluation of the antibiotic susceptibility in five human A. muciniphila isolates. Genomic mining for antimicrobial resistance genes and MICs determinations revealed that only one strain harboring tetW gene showed resistance to tetracycline, whereas all A. muciniphila strains showed low sensitivity to ciprofloxacin and aminoglycosides with no genotypic correlation. Although all strains harbor the gene adeF, encoding for a subunit of the resistance-nodulation-cell division efflux pump system, potentially involved in ciprofloxacin resistance, the susceptibility towards ciprofloxacin determined in presence of efflux pump inhibitors was not affected. Overall, our outcomes revealed the importance to extend the antibiotic susceptibility test to a larger number of new isolates of A. muciniphila to better assess the safety aspects of this species.

Genomic Characterization of Antimicrobial-Resistant Salmonella enterica in Duck, Chicken, and Pig Farms and Retail Markets in Eastern China

Antimicrobial-resistant Salmonella enterica poses a significant public health concern worldwide. However, the dissemination of Salmonella enterica among food animals in eastern China has not been fully addressed. Here, we demonstrated the antimicrobial resistance (AMR) patterns and the whole-genome characterization of 105 S. enterica isolates from 1,480 fecal samples and anal swabs collected from 22 different farms (chickens, ducks, and pigs) and two live animal markets located in Zhejiang and Fujian Provinces in eastern China in 2019. The prevalence of isolates in duck farms (19.17%, 23/120) was statistically significantly higher (P < 0.001) than that in chicken farms (6.61%, 37/523) and pig farms (3.50%, 7/200). Among these isolates, 75.26% (79/105) were multidrug resistant, with the highest rates of resistance to tetracycline (76.20%) and ampicillin (67.62%) and the lowest resistance rate to meropenem (0.00%). The serotypes were consistent with sequence types and were closely related to the sampling animal species and sites. S. enterica serotype Kentucky (20.95%, 22/105) was the most frequent serotype and harbored more AMR patterns and genes than others. Furthermore, IncFII(S) and IncHI2 were the most prevalent replicons. A total of 44 acquired AMR genes were found. Among those genes, aac(6')-Iaa, blaTEM-1B, floR, dfrA14, fosA7, mph(A), qnrS1, sul1, tet(A), and ARR-3 were the dominant AMR genes mediating the AMR toward aminoglycosides, β-lactams, phenicol, trimethoprim, fosfomycin, macrolide, quinolone, sulfonamides, tetracycline, and rifampin, respectively. The consistency of acquired AMR genes with AMR phenotypes for ampicillin, ceftiofur, ceftazidime, meropenem, sulfamethoxazole-trimethoprim, and tetracycline was >90%. Together, our study highlights the application of whole-genome sequencing to assess veterinary public health threats. IMPORTANCE Public health is a significant concern in China, and the foodborne pathogen Salmonella, which is spread via the animal-borne food chain, plays an important role in the overall disease burden in China annually. The development of advanced sequencing technologies has introduced a new way of understanding emerging pathogens. However, the routine surveillance application of this method in China remains in its infancy. Here, we applied a pool of all isolates from the prevalence data in Zhejiang and Fujian for whole-genome sequencing and combined these data with the cutting-edge bioinformatic analysis pipeline for one-step determination of the complete genetic makeup for all 105 genomes. The illustrated method could provide a cost-effective approach, without labor-intensive laboratory characterization, for predicting serotypes, genotypes, plasmid types, antimicrobial resistance genes, and virulence genes, and thus would provide essential knowledge for emerging pathogens. Our findings and perspectives are essential for delivering updated knowledge on foodborne pathogens in an understudied region in China.

Whole genome sequencing reveals antimicrobial resistance determinants (AMR genes) of Salmonella enterica recovered from raw chicken and ready-to-eat leaves imported into England between 2014 and 2019

AIMS

To compare the antimicrobial resistance (AMR) genes in a genetically diverse group of Salmonella enterica recovered from foods imported into England between 2014 and 2018.

METHODS AND RESULTS

Whole genome sequence was used to detect AMR genes or chromosomal mutations associated with AMR in Salmonella recovered from edible leaves imported from Asia (n = 115) as compared to Salmonella (n = 231) isolated from raw chicken, 74% originated from South America. Among isolates from edible leaves, three (3%) showed resistance to at least one antimicrobial agent, two (2%) of which were multidrug resistant (MDR, resistance to three or more antimicrobial classes). Resistance to at least one antimicrobial agent was detected in 214 (93%) in the chicken isolates, with 164 (71%) showing MDR. Genetic diversity and AMR profiles were highly heterogeneous across the different serovars.

CONCLUSIONS

Resistance was rare among the Salmonella isolates from edible leaves but common (including MDR) among those from raw chicken.

SIGNIFICANCE AND IMPACT OF THE STUDY

Surveillance of AMR in imported foods is essential for monitoring the risk of transmission of resistance from the food chain to humans and provides added public health value to pre-existing controls of the food chain.

Genome-Based Assessment of Antimicrobial Resistance and Virulence Potential of Isolates of Non-Pullorum/Gallinarum Salmonella Serovars Recovered from Dead Poultry in China

Paratyphoid avian salmonellosis is considered one of the leading causes of poultry death, resulting in significant economic losses to poultry industries worldwide. In China, especially in Shandong province, the leading producer of poultry products, several recurrent outbreaks of avian salmonellosis have been reported during the last decade where the precise causal agent remains unknown. Moreover, the establishment of earlier and more accurate recognition of pathogens is a key factor to prevent the further dissemination of resistant and/or hypervirulent clones. Here, we aim to use whole-genome sequencing combined with in silico toolkits to provide the genomic features of the antimicrobial resistance and virulence potential of 105 regionally representative non-Pullorum/Gallinarum Salmonella isolates recovered from dead poultry between 2008 and 2019 in Shandong, China. Additionally, phenotypic susceptibility to a panel of 15 antibiotics representing 11 classes was assessed by the broth microdilution method. In this study, we identified eight serovars and nine multilocus sequence typing (MLST) types, with Salmonella enterica serovar Enteritidis sequence type 11 (ST11) being the most prevalent (84/105; 80%). Based on their phenotypic antimicrobial resistance, 77.14% of the isolates were defined as multidrug resistant (≥3 antimicrobial classes), with the detection of one S. Enteritidis isolate that was resistant to the 11 classes. The highest rates of resistance were observed against nalidixic acid (97.14%) and ciprofloxacin (91.43%), followed by ampicillin (71.43%), streptomycin (64.77%), and tetracycline (60%). Genomic characterization revealed the presence of 41 resistance genes, with an alarmingly high prevalence of blaTEM-1B (60%), in addition to genomic mutations affecting the DNA gyrase (gyrA) and DNA topoisomerase IV (parC) genes, conferring resistance to quinolones. The prediction of plasmid replicons detected 14 types, with a dominance of IncFIB(S)_1 and IncFII(S)_1 (87.62% for both), while the IncX1 plasmid type was considered the key carrier of antimicrobial resistance determinants. Moreover, we report the detection of critical virulence genes, including cdtB, rck, sodCI, pef, and spv, in addition to the typical determinants for Salmonella pathogenicity island 1 (SPI-1) and SPI-2. Furthermore, phylogenomic analysis revealed the detection of three intra-farm and five inter-farm transmission events. Overall, the detection of Salmonella isolates presenting high antimicrobial resistance and harboring different critical virulence genes is of major concern, which requires the urgent implementation of effective strategies to mitigate non-Pullorum/Gallinarum avian salmonellosis. IMPORTANCE Avian salmonellosis is one of the leading global causes of poultry death, resulting in substantial economic losses in China (constituting 9% of overall financial losses). In Shandong province, a top poultry producer (30% of the overall production in China, with 15% being exported to the world), extensive outbreaks of avian salmonellosis have been reported in the past decade where the causal agents or exact types remain rarely addressed. From approximately 2008 to 2019, over 2,000 Salmonella strains were isolated and identified from dead poultry during routine surveillance of 95 poultry farms covering all 17 cities in Shandong. Approximately 1,500 isolates were confirmed to be of non-Pullorum/Gallinarum Salmonella serovars. There is an urgent need to understand the mechanisms behind the implication of zoonotic Salmonella serovars in systemic infections of poultry. Here, we analyzed populations of clinically relevant isolates of non-Pullorum/Gallinarum Salmonella causing chicken death in China by a whole-genome sequencing approach and determined that antimicrobial-resistant Salmonella Enteritidis remained the major cause in the past decades.

WGS-Based Lineage and Antimicrobial Resistance Pattern of Salmonella Typhimurium Isolated during 2000-2017 in Peru

Salmonella Typhimurium is associated with foodborne diseases worldwide, including in Peru, and its emerging antibiotic resistance (AMR) is now a global public health problem. Therefore, country-specific monitoring of the AMR emergence is vital to control this pathogen, and in these aspects, whole genome sequence (WGS)—based approaches are better than gene-based analyses. Here, we performed the antimicrobial susceptibility test for ten widely used antibiotics and WGS-based various analyses of 90 S. Typhimurium isolates (human, animal, and environment) from 14 cities of Peru isolated from 2000 to 2017 to understand the lineage and antimicrobial resistance pattern of this pathogen in Peru. Our results suggest that the Peruvian isolates are of Typhimurium serovar and predominantly belong to sequence type ST19. Genomic diversity analyses indicate an open pan-genome, and at least ten lineages are circulating in Peru. A total of 48.8% and 31.0% of isolates are phenotypically and genotypically resistant to at least one antibiotic, while 12.0% are multi-drug resistant (MDR). Genotype−phenotype correlations for ten tested drugs show >80% accuracy, and >90% specificity. Sensitivity above 90% was only achieved for ciprofloxacin and ceftazidime. Two lineages exhibit the majority of the MDR isolates. A total of 63 different AMR genes are detected, of which 30 are found in 17 different plasmids. Transmissible plasmids such as lncI-gamma/k, IncI1-I(Alpha), Col(pHAD28), IncFIB, IncHI2, and lncI2 that carry AMR genes associated with third-generation antibiotics are also identified. Finally, three new non-synonymous single nucleotide variations (SNVs) for nalidixic acid and eight new SNVs for nitrofurantoin resistance are predicted using genome-wide association studies, comparative genomics, and functional annotation. Our analysis provides for the first time the WGS-based details of the circulating S. Typhimurium lineages and their antimicrobial resistance pattern in Peru.

Harmonisation of in-silico next-generation sequencing based methods for diagnostics and surveillance

Improvements in cost and speed of next generation sequencing (NGS) have provided a new pathway for delivering disease diagnosis, molecular typing, and detection of antimicrobial resistance (AMR). Numerous published methods and protocols exist, but a lack of harmonisation has hampered meaningful comparisons between results produced by different methods/protocols vital for global genomic diagnostics and surveillance. As an exemplar, this study evaluated the sensitivity and specificity of five well-established in-silico AMR detection software where the genotype results produced from running a panel of 436 Escherichia coli were compared to their AMR phenotypes, with the latter used as gold-standard. The pipelines exploited previously known genotype–phenotype associations. No significant differences in software performance were observed. As a consequence, efforts to harmonise AMR predictions from sequence data should focus on: (1) establishing universal minimum to assess performance thresholds (e.g. a control isolate panel, minimum sensitivity/specificity thresholds); (2) standardising AMR gene identifiers in reference databases and gene nomenclature; (3) producing consistent genotype/phenotype correlations. The study also revealed limitations of in-silico technology on detecting resistance to certain antimicrobials due to lack of specific fine-tuning options in bioinformatics tool or a lack of representation of resistance mechanisms in reference databases. Lastly, we noted user friendliness of tools was also an important consideration. Therefore, our recommendations are timely for widespread standardisation of bioinformatics for genomic diagnostics and surveillance globally.

Comparative Genomic Analysis Discloses Differential Distribution of Antibiotic Resistance Determinants between Worldwide Strains of the Emergent ST213 Genotype of Salmonella Typhimurium

Salmonella enterica constitutes a global public health concern as one of the main etiological agents of human gastroenteritis. The Typhimurium serotype is frequently isolated from human, animal, food, and environmental samples, with its sequence type 19 (ST19) being the most widely distributed around the world as well as the founder genotype. The replacement of the ST19 genotype with the ST213 genotype that has multiple antibiotic resistance (MAR) in human and food samples was first observed in Mexico. The number of available genomes of ST213 strains in public databases indicates its fast worldwide dispersion, but its public health relevance is unknown. A comparative genomic analysis conducted as part of this research identified the presence of 44 genes, 34 plasmids, and five point mutations associated with antibiotic resistance, distributed across 220 genomes of ST213 strains, indicating the MAR phenotype. In general, the grouping pattern in correspondence to the presence/absence of genes/plasmids that confer antibiotic resistance cluster the genomes according to the geographical origin where the strain was isolated. Genetic determinants of antibiotic resistance group the genomes of North America (Canada, Mexico, USA) strains, and suggest a dispersion route to reach the United Kingdom and, from there, the rest of Europe, then Asia and Oceania. The results obtained here highlight the worldwide public health relevance of the ST213 genotype, which contains a great diversity of genetic elements associated with MAR.

Genomic and Evolutionary Analysis of Salmonella enterica Serovar Kentucky Sequence Type 198 Isolated From Livestock In East Africa

Since its emergence in the beginning of the 90’s, multidrug-resistant (MDR) Salmonella enterica subsp. enterica serovar Kentucky has become a significant public health problem, especially in East Africa. This study aimed to investigate the antimicrobial resistance profile and the genotypic relatedness of Salmonella Kentucky isolated from animal sources in Ethiopia and Kenya (n=19). We also investigated population evolutionary dynamics through phylogenetic and pangenome analyses with additional publicly available Salmonella Kentucky ST198 genomes (n=229). All the 19 sequenced Salmonella Kentucky isolates were identified as ST198. Among these isolates, the predominant genotypic antimicrobial resistance profile observed in ten (59.7%) isolates included the aac(3)-Id, aadA7, strA-strB, bla_TEM-1B, sul1, and tet(A) genes, which mediated resistance to gentamicin, streptomycin/spectinomycin, streptomycin, ampicillin, sulfamethoxazole and tetracycline, respectively; and gyrA and parC mutations associated to ciprofloxacin resistance. Four isolates harbored plasmid types Incl1 and/or Col8282; two of them carried both plasmids. Salmonella Pathogenicity islands (SPI-1 to SPI-5) were highly conserved in the 19 sequenced Salmonella Kentucky isolates. Moreover, at least one Pathogenicity Island (SPI 1–4, SPI 9 or C63PI) was identified among the 229 public Salmonella Kentucky genomes. The phylogenetic analysis revealed that almost all Salmonella Kentucky ST198 isolates (17/19) stemmed from a single strain that has accumulated ciprofloxacin resistance-mediating mutations. A total of 8,104 different genes were identified in a heterogenic and still open Salmonella Kentucky ST198 pangenome. Considering the virulence factors and antimicrobial resistance genes detected in Salmonella Kentucky, the implications of this pathogen to public health and the epidemiological drivers for its dissemination must be investigated.

Integration of genomics in surveillance and risk assessment for outbreak investigation

Keeping food safe is a challenge that needs continuous surveillance for the sake of consumers' health. The main issue when a food-borne pathogen outbreak occurs is represented by the identification of the source(s) of contamination. Delivering this information in a timely manner helps to control the problem, with positive outcomes for everyone, especially for the consumers, whose health is in this way preserved, and for the stakeholders involved in food production and distribution, who could face enormous economic losses if recalls or legal issues occur. Whole genome sequencing (WGS) is a tool recently implemented for the characterisation of isolates and the study of outbreaks because of its higher efficiency and faster results, when compared to traditional typing methods. Lower sequencing costs and the development of many bioinformatic tools helped its spread, and much more attention has been given to its use for outbreak investigation. It is important to reach a certain level of standardisation, though, for ensuring result reproducibility and interoperability. Moreover, nowadays it is possible, if not mandatory for Open Science Practices, to share WGS data in publicly available databases, where raw reads, assembled genomes and their corresponding metadata can be easily found and downloaded. The scope of this Fellowship was to provide the Fellow all the training necessary for successfully integrating genomics to surveillance and risk assessment of food-borne pathogens from farm to fork.

Enhancing predictions of antimicrobial resistance of pathogens by expanding the potential resistance gene repertoire using a pan-genome-based feature selection approach

Background

Predicting which pathogens might exhibit antimicrobial resistance (AMR) based on genomics data is one of the promising ways to swiftly and precisely identify AMR pathogens. Currently, the most widely used genomics approach is through identifying known AMR genes from genomic information in order to predict whether a pathogen might be resistant to certain antibiotic drugs. The list of known AMR genes, however, is still far from comprehensive and may result in inaccurate AMR pathogen predictions. We thus felt the need to expand the AMR gene set and proposed a pan-genome-based feature selection method to identify potential gene sets for AMR prediction purposes.

Results

By building pan-genome datasets and extracting gene presence/absence patterns from four bacterial species, each with more than 2000 strains, we showed that machine learning models built from pan-genome data can be very promising for predicting AMR pathogens. The gene set selected by the eXtreme Gradient Boosting (XGBoost) feature selection approach further improved prediction outcomes, and an incremental approach selecting subsets of XGBoost-selected features brought the machine learning model performance to the next level. Investigating selected gene sets revealed that on average about 50% of genes had no known function and very few of them were known AMR genes, indicating the potential of the selected gene sets to expand resistance gene repertoires.

Conclusions

We demonstrated that a pan-genome-based feature selection approach is suitable for building machine learning models for predicting AMR pathogens. The extracted gene sets may provide future clues to expand our knowledge of known AMR genes and provide novel hypotheses for inferring bacterial AMR mechanisms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-022-04666-2.

Genomic Screening of Antimicrobial Resistance Markers in UK and US Campylobacter Isolates Highlights Stability of Resistance over an 18-Year Period

Campylobacter jejuni and Campylobacter coli are important bacterial causes of human foodborne illness. Despite several years of reduced antibiotics usage in livestock production in the United Kingdom (UK) and United States (US), a high prevalence of antimicrobial resistance (AMR) persists in Campylobacter. Both countries have instigated genome sequencing-based surveillance programs for Campylobacter, and in this study, we have identified AMR genes in 32,256 C. jejuni and 8,776 C. coli publicly available genome sequences to compare the prevalence and trends of AMR in Campylobacter isolated in the UK and US between 2001 and 2018. AMR markers were detected in 68% of C. coli and 53% of C. jejuni isolates, with 15% of C. coli isolates being multidrug resistant (MDR), compared to only 2% of C. jejuni isolates. The prevalence of aminoglycoside, macrolide, quinolone, and tetracycline resistance remained fairly stable from 2001 to 2018 in both C. jejuni and C. coli, but statistically significant differences were observed between the UK and US. There was a statistically significant higher prevalence of aminoglycoside and tetracycline resistance for US C. coli and C. jejuni isolates and macrolide resistance for US C. coli isolates. In contrast, UK C. coli and C. jejuni isolates showed a significantly higher prevalence of quinolone resistance. Specific multilocus sequence type (MLST) clonal complexes (e.g., ST-353/464) showed >95% quinolone resistance. This large-scale comparison of AMR prevalence has shown that the prevalence of AMR remains stable for Campylobacter in the UK and the US. This suggests that antimicrobial stewardship and restricted antibiotic usage may help contain further expansion of AMR prevalence in Campylobacter but are unlikely to reduce it in the short term.

Antimicrobial Resistance Profiles of Non-typhoidal Salmonella From Retail Meat Products in California, 2018

Non-typhoidal Salmonella remains a leading cause of foodborne illness in the United States, with food animal products serving as a key conduit for transmission. The emergence of antimicrobial resistance (AMR) poses an additional public health concern warranting better understanding of its epidemiology. In this study, 958 retail meat samples collected from January to December 2018 in California were tested for Salmonella. From multivariable logistic regression, there was a 6.47 (90% CI 2.29–18.27), 3.81 (90% CI 1.29–11.27), and 3.12 (90% CI 1.03–9.45) higher odds of contamination in samples purchased in the fall, spring, and summer than in winter months, respectively, and a 3.70 (90% CI 1.05–13.07) higher odds in ground turkey compared to pork samples. Fourteen distinct serotypes and 17 multilocus sequence types were identified among the 43 isolates recovered, with S. Kentucky (25.58%), S. Reading (18.60%), S. Infantis (11.63%), and S. Typhimurium (9.30%) comprising the top serotypes. High prevalence of resistance was observed in retail chicken isolates for streptomycin (12/23, 52.17%) and tetracycline (12/23, 52.17%), in ground turkey isolates for ampicillin (8/15, 53.34%), and in ground beef isolates for nalidixic acid (2/3, 66.67%). Fourteen (32.56%) were susceptible to all antimicrobials tested, 11 (25.58%) were resistant to one drug, and 12 (27.91%) were resistant to two drugs. The remaining six isolates (13.95%) were multidrug-resistant (MDR, ≥3 drug classes) S. Infantis (n = 4), S. Reading (n = 1), and S. Kentucky (n = 1). Whole-genome sequencing (WGS) identified 16 AMR genes and 17 plasmid replicons, including bla_CTX–M–65 encoding ceftriaxone resistance and a D87Y mutation in gyrA conferring resistance to nalidixic acid and reduced susceptibility to ciprofloxacin. The IncFIB(pN55391) replicon previously identified in connection to the worldwide dissemination of pESI-like mega plasmid carriage in an emerged S. Infantis clone was detected in four of the six MDR isolates. Genotypes from WGS showed high concordance with phenotype with overall sensitivity and specificity of 95.31% and 100%, respectively. This study provides insight into the AMR profiles of a diversity of Salmonella serotypes isolated from retail meat products in California and highlights the value of routine retail food surveillance for the detection and characterization of AMR in foodborne pathogens.

A roadmap for the generation of benchmarking resources for antimicrobial resistance detection using next generation sequencing

Next Generation Sequencing technologies significantly impact the field of Antimicrobial Resistance (AMR) detection and monitoring, with immediate uses in diagnosis and risk assessment. For this application and in general, considerable challenges remain in demonstrating sufficient trust to act upon the meaningful information produced from raw data, partly because of the reliance on bioinformatics pipelines, which can produce different results and therefore lead to different interpretations. With the constant evolution of the field, it is difficult to identify, harmonise and recommend specific methods for large-scale implementations over time. In this article, we propose to address this challenge through establishing a transparent, performance-based, evaluation approach to provide flexibility in the bioinformatics tools of choice, while demonstrating proficiency in meeting common performance standards. The approach is two-fold: first, a community-driven effort to establish and maintain “live” (dynamic) benchmarking platforms to provide relevant performance metrics, based on different use-cases, that would evolve together with the AMR field; second, agreed and defined datasets to allow the pipelines’ implementation, validation, and quality-control over time. Following previous discussions on the main challenges linked to this approach, we provide concrete recommendations and future steps, related to different aspects of the design of benchmarks, such as the selection and the characteristics of the datasets (quality, choice of pathogens and resistances, etc.), the evaluation criteria of the pipelines, and the way these resources should be deployed in the community.

Characteristics and Global Occurrence of Human Pathogens Harboring Antimicrobial Resistance in Food Crops: A Scoping Review

Background

The role of the crop environment as a conduit for antimicrobial resistance (AMR) through soil, water, and plants has received less attention than other sectors. Food crops may provide a link between the agro-environmental reservoir of AMR and acquisition by humans, adding to existing food safety hazards associated with microbial contamination of food crops.

Objectives

The objectives of this review were: (1) to use a systematic methodology to characterize AMR in food crop value chains globally, and (2) to identify knowledge gaps in understanding exposure risks to humans.

Methods

Four bibliographic databases were searched using synonyms of AMR in food crop value chains. Following two-stage screening, phenotypic results were extracted and categorized into primary and secondary combinations of acquired resistance in microbes of concern based on established prioritization. Occurrence of these pathogen-AMR phenotype combinations were summarized by sample group, value chain stage, and world region. Sub-analyses on antimicrobial resistance genes (ARG) focused on extended-spectrum beta-lactamase and tetracycline resistance genes.

Results

Screening of 4,455 citations yielded 196 studies originating from 49 countries, predominantly in Asia (89 studies) and Africa (38). Observations of pathogen-phenotype combinations of interest were reported in a subset of 133 studies (68%). Primary combinations, which include resistance to antimicrobials of critical importance to human medicine varied from 3% (carbapenem resistance) to 13% (fluoroquinolones), whereas secondary combinations, which include resistance to antimicrobials also used in agriculture ranged from 14% (aminoglycoside resistance) to 20% (aminopenicillins). Salad crops, vegetables, and culinary herbs were the most sampled crops with almost twice as many studies testing post-harvest samples. Sub-analysis of ARG found similar patterns corresponding to phenotypic results.

Discussion

These results suggest that acquired AMR in opportunistic and obligate human pathogens is disseminated throughout food crop value chains in multiple world regions. However, few longitudinal studies exist and substantial heterogeneity in sampling methods currently limit quantification of exposure risks to consumers. This review highlights the need to include agriculturally-derived AMR in monitoring food safety risks from plant-based foods, and the challenges facing its surveillance.