Antimicrobial Resistance in Nontyphoidal Salmonella

Synanthropic rodents and shrews are reservoirs of zoonotic bacterial pathogens and act as sentinels for antimicrobial resistance spillover in the environment: A study from Puducherry, India

Antimicrobial resistance (AMR) is a global public health concern and needs to be monitored for control. In this study, synanthropic rodents trapped from humans and animal habitats in Puducherry, India, were screened as sentinels for bacterial pathogens of public health importance and antimicrobial resistance spillover. From the trapped rodents and shrews (n = 100) pathogens viz., Staphylococcus sp, E. coli and Salmonella sp were isolated from oropharyngeal and rectal swabs on Mannitol salt, Mac Conkey and Xylose lysine deoxycholate media respectively. The AMR genes in these isolates were screened by PCR. A total of 76, S. aureus and 19, Staphylococcus non aureus were isolated. E. coli was isolated in 89 samples and among the Salmonella sp (n = 59), 16, were S. enteritidis and 29, were S. typhimurium. A total of 46 MRSA isolates with mec A (n = 40) and mec C (n = 6) were detected. Also, 36.84% and 5.3% Staphylococcus non aureus isolates were tested to have mec A and mec C genes. AMR genes encoding ESBL [blaTEM in 21, blaSHV in 45 and blaCTX-M in 11] was tested positive in 77 E. coli isolates. Among, Salmonella isolates 44/45 were screened to have AMR genes [tet in 13, sul3 & sul4 in 20 and qnrA in 11]. Antibiotic sensitivity test confirmed the antimicrobial resistance. Isolation of pathogens of public health importance and demonstration of genetic elements conferring antimicrobial resistance in the synanthropic rodents confirms that they act as reservoirs and appropriate sentinels to monitor AMR spillover in the environment.

Antimicrobial resistance and genetic relatedness of Salmonella serotypes isolated from food, asymptomatic carriers, and clinical cases in Shiyan, China

Salmonella is a primary cause of foodborne diseases globally. Despite food contamination and clinical infections garnering substantial attention and research, asymptomatic Salmonella carriers, potential sources of infection, have been comparatively overlooked. In this study, we conducted a comparative analysis of serotype distribution, antimicrobial resistance phenotypes, and genetic profiles of archived Salmonella strains isolated from food (26), asymptomatic carriers (41), and clinical cases (47) in Shiyan City, China. Among the 114 Salmonella strains identified, representing 31 serotypes and 34 Sequence Types (STs), the most prevalent serovars included Typhimurium, Derby, Enteritidis, Thompson, and London, with the most predominant STs being ST11, ST40, ST26, ST34, and ST155. Antimicrobial resistance testing revealed that all strains were only sensitive to meropenem, with 74.6% showing antimicrobial resistance (AMR) and 53.5% demonstrating multidrug resistance (MDR). Strains resistant to five and six classes of antibiotics were the most common. Pearson's chi-square test showed no statistically significant difference in the occurrence of AMR (p = 0.105) or MDR (p = 0.326) among Salmonella isolates from the three sources. Our findings underscore associations and diversities among Salmonella strains isolated from food, asymptomatic carriers, and clinical patients, emphasizing the need for increased vigilance towards asymptomatic Salmonella carriers by authorities.

Epidemiological and Whole Genome Sequencing Analysis of Restaurant Salmonella Enteritidis Outbreak Associated with an Infected Food Handler in Jiangxi Province, China, 2023

In China, Salmonella is one of the most frequent causes of bacterial gastroenteritis, and food handlers in restaurants as an important contaminated source were rarely reported. In May 2023, an outbreak of Salmonella enterica serovar Enteritidis infection in a restaurant in Jiangxi Province, China, was investigated. Cases were interviewed. Stool samples from cases, anal swabs from restaurant employees, suspicious raw food materials, and semifinished food were collected and examined. Pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS) were performed to determine the relatedness of the pathogen isolates. Antimicrobial resistance genes and virulence genes of isolates were analyzed by WGS. The antimicrobial profile of the isolates was detected by broth microdilution, which involved 20 different antibiotics. Among the 31 patrons, 26 showed gastrointestinal symptoms. Five Salmonella Enteritidis strains were isolated from patients (2), semifinished food (2), and food handler (1). The results of PFGE and single-nucleotide polymorphism showed that these five isolates were identical clones. These findings demonstrated that this outbreak was a restaurant Salmonella Enteritidis outbreak associated with an infected food handler. The rates of resistance to nalidixic acid and colistin and intermediate resistance to ciprofloxacin were 100%, 80%, and 100%, respectively. These outbreak isolates harbored point mutation gyrA p.D87G. The cause of inconsistency between the genotype and phenotype of resistance was deeply discussed. A total of 107 virulence genes were found in each isolate, with many being associated with Salmonella pathogenicity island (SPI)-1 and SPI-2. As an overlooked contamination source, infected food handlers can easily cause large-scale outbreaks. This outbreak highlighted that the government should enhance the training and supervision of food hygiene and safety for food handlers to prevent foodborne outbreaks.

Epidemiology of Salmonella enterica subspecies enterica serotypes, isolated from imported, farmed and feral poultry in the Cayman Islands

Non-typhoidal Salmonellae (NTS) are common foodborne pathogens throughout the world causing acute gastroenteritis. Compared to North America and Europe, there is little information on NTS in the Caribbean. Here we investigated the prevalence and characteristics of NTS present in the local poultry of the Cayman Islands to determine the public health risk. In total, we collected 156 samples. These were made up of boot swabs of 31 broiler farms and 31 layer farms (62 samples), paper bedding from 45 imported chick boxes, and 49 pooled cecum samples from feral chickens, each sample representing 10 individual chickens. Salmonella was isolated using the ISO 6579 protocol and isolates were characterized using Whole Genome Sequencing (WGS) analysis. Eighteen Salmonella isolates were obtained and comprised six S. enterica subspecies enterica serotypes and one subspecies houtenae serotype. Serotypes were: S. Kentucky (n = 9), S. Saintpaul (n = 5), S. Javiana (n = 1), S. Senftenberg (n = 1), S. Poona (n = 1) and S. Agona (n = 1). S. Kentucky strains were all ST152 and clonally related to poultry strains from the United states. S. Saintpaul ST50 strains showed clonality to North American strains. Over half of the strains (n = 11) contained resistance genes to at least two antibiotic groups and five strains were MDR, mainly those from imported day-old chicks. The blaCMY-2 gene was found in S. Kentucky from day-old chicks. Strains from feral poultry had no acquired AMR genes. While serotypes from feral poultry have been identified in human infections, they pose minimal risk due to their low virulence.

High levels of multidrug-resistant isolates of genetically similar Salmonella 1,4, [5],12:I:- from Brazil between 1983 and 2020

Introduction. Salmonella 1,4, [5],12:i:- strains with different antimicrobial resistance profiles have been associated with foodborne disease outbreaks in several countries. In Brazil, S. 1,4, [5],12:i:- was identified as one of the most prevalent serovars in São Paulo State during 2004-2020.Gap Statement. However, few studies have characterized this serovar in Brazil.Aim. This study aimed to determine the antimicrobial resistance profiles of S. 1,4, [5],12:i:- strains isolated from different sources in Southeast Brazil and compare their genetic diversity.Methodology. We analysed 113 S. 1,4, [5],12:i:- strains isolated from humans (n=99), animals (n=7), food (n=5) and the environment (n=2) between 1983 and 2020. Susceptibility testing against 13 antimicrobials was performed using the disc diffusion method for all the strains. Plasmid resistance genes and mutations in the quinolone resistance-determining regions were identified in phenotypically fluoroquinolone-resistant strains. Molecular typing was performed using enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) for all strains and multilocus sequence typing (MLST) for 40 selected strains.Results. Of the 113 strains, 54.87 % were resistant to at least one antimicrobial. The highest resistance rates were observed against ampicillin (51.33 %), nalidixic acid (39.82 %) and tetracycline (38.05 %). Additionally, 39 (34.51 %) strains were classified as multidrug-resistant (MDR). Nine fluoroquinolone-resistant strains exhibited the gyrA mutation (Ser96→Tyr96) and contained the qnrB gene. The 113 strains were grouped into two clusters using ERIC-PCR, and most of strains were present in one cluster, with a genetic similarity of ≥80 %. Finally, 40 strains were typed as ST19 using MLST.Conclusion. The prevalence of MDR strains is alarming because antimicrobial treatment against these strains may lead to therapeutic failure. Furthermore, the ERIC-PCR and MLST results suggested that most strains belonged to one main cluster. Thus, a prevalent subtype of Salmonella 1,4, [5],12:i:- strains has probably been circulating among different sources in São Paulo, Brazil, over decades.

Discovery of new dibenzodiazepine derivatives as antibacterials against intracellular bacteria

The emergence and spread of multidrug-resistant bacteria underscore the critical need for novel antibacterial interventions. In our screening of 12 synthesized thienobenzodiazepines, pyridobenzodiazepines, and dibenzodiazepines, we successfully identified a small molecule compound SW33. Notably, SW33 demonstrated potent inhibitory activity against intracellular multidrug-resistant and fluoroquinolone-resistant strains of S. typhimurium in both macrophages and epithelial cells. Furthermore, SW33 was also effective against intramacrophagic Salmonella typhi, Yersinia enterocolitica, and Listeria monocytogenes. These significant findings suggest that SW33 possesses broad-spectrum activity against intracellular bacteria.

Occurrence, genetic diversity and resistance profiles of Salmonella enterica from Brazilian sausages collected at production facilities

This study aimed to investigate the occurrence and the genetic diversity of Salmonella enterica subsp. enterica in sausages from Southern Brazil, evaluate virulence genes and determine the phenotypic and genotypic basis of antimicrobial and sanitizer resistance. Salmonella was detected in sausage samples with an overall prevalence of 5.5%. The prevalent serovars were S. Infantis and S. Rissen. Pulsed-field gel electrophoresis (PFGE) analysis yielded nine distinct PFGE profiles, and some of them were recurrently recovered in the same establishment on different dates. Among tested isolates, 28.5% showed resistance to at least one antimicrobial agent and a multidrug-resistance (MDR) profile was observed in 21.4%. Resistance occurred most frequently to ampicillin, sulfonamide, trimethoprim/sulfamethoxazole, and trimethoprim. Regarding the genotypic antimicrobial resistance profile, S. Schwarzengrund carried tet(B), strA, strB, and sul2 genes. Benzalkonium chloride and chlorhexidine were more effective than peracetic acid and sodium hypochlorite, showing lower minimum inhibitory concentration values. Six Salmonella serovars were found, demonstrating a potential risk of salmonellosis associated with consuming this food. Salmonella carrying virulence genes, MDR profile, and tolerance to sanitizers is a public health concern and a challenge for the food industry, suggesting that new strategies should be developed to control this pathogen.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05809-w.

Genomic analysis of almost 8,000 Salmonella genomes reveals drivers and landscape of antimicrobial resistance in China

IMPORTANCE

We established the largest Salmonella genome database from China and presented the landscape and spatiotemporal dynamics of antimicrobial resistance genes. We also found that economic, climatic, and social factors can drive the rise of antimicrobial resistance. The Chinese local Salmonella genome database version 2 was released as an open-access database (https://nmdc.cn/clsgdbv2) and thus can assist surveillance studies across the globe. This database will help inform interventions for AMR, food safety, and public health.

Exploration of the novel fluoroquinolones with high inhibitory effect against quinolone-resistant DNA gyrase of Salmonella Typhimurium

IMPORTANCE

Quinolone-resistant nontyphoidal Salmonella is a pressing public health concern, demanding the exploration of novel treatments. In this study, we focused on two innovative synthetic fluoroquinolones, WQ-3034 and WQ-3154. Our findings revealed that these new compounds demonstrate potent inhibitory effects, even against mutant strains that cause resistance to existing quinolones. Hence, WQ-3034 and WQ-3154 could potentially be effective therapeutic agents against quinolone-resistant Salmonella Typhimurium. Furthermore, the data obtained in this study will be baseline information for antimicrobial drug development.

Genomic analysis of the MLST population structure and antimicrobial resistance genes associated with Salmonella enterica in Mexico

Salmonella enterica is one of the most commonly reported foodborne pathogens by public health agencies worldwide. In this study, the multilocus sequence typing (MLST) population structure and frequency of antimicrobial resistance (AMR) genes were evaluated in S. enterica strains from Mexico (n = 2561). The most common sources of isolation were food (44.28%), environment (27.41%), animal-related (24.83%), and human (3.48%). The most prevalent serovars were Newport (8.51%), Oranienburg (7.03%), Anatum (5.78%), Typhimurium (5.12%), and Infantis (4.57%). As determined by the 7-gene MLST scheme, the most frequent sequence types were ST23, ST64, and ST32. The core genome MLST scheme identified 132 HC2000 and 195 HC900 hierarchical clusters, with the HC2000_2 cluster being the most prevalent in Mexico (n = 256). A total of 78 different AMR genes belonging to 13 antimicrobial classes were detected in 638 genomic assemblies of S. enterica. The most frequent class was aminoglycosides (31.76%), followed by tetracyclines (12.53%) and sulfonamides (11.91%). These results can help public health agencies in Mexico prioritize their efforts and resources to increase the genomic sequencing of circulating Salmonella strains. Additionally, they provide valuable information for local and global public health efforts to reduce the impact of foodborne diseases and AMR.

Serovars, Virulence and Antimicrobial Resistance Genes of Non-Typhoidal Salmonella Strains from Dairy Systems in Mexico

Salmonella isolated from dairy farms has a significant effect on animal health and productivity. Different serogroups of Salmonella affect both human and bovine cattle causing illness in both reservoirs. Dairy cows and calves can be silent Salmonella shedders, increasing the possibility of dispensing Salmonella within the farm. The aim of this study was to determine the genomic characteristics of Salmonella isolates from dairy farms and to detect the presence of virulence and antimicrobial resistance genes. A total of 377 samples were collected in a cross-sectional study from calves, periparturient cow feces, and maternity beds in 55 dairy farms from the states of Aguascalientes, Baja California, Chihuahua, Coahuila, Durango, Mexico, Guanajuato, Hidalgo, Jalisco, Queretaro, San Luis Potosi, Tlaxcala, and Zacatecas. Twenty Salmonella isolates were selected as representative strains for whole genome sequencing. The serological classification of the strains was able to assign groups to only 12 isolates, but with only 5 of those being consistent with the genomic serotyping. The most prevalent serovar was Salmonella Montevideo followed by Salmonella Meleagridis. All isolates presented the chromosomal aac(6')-Iaa gene that confers resistance to aminoglycosides. The antibiotic resistance genes qnrB19, qnrA1, sul2, aph(6)-Id, aph(3)-ld, dfrA1, tetA, tetC, flor2, sul1_15, mph(A), aadA2, blaCARB, and qacE were identified. Ten pathogenicity islands were identified, and the most prevalent plasmid was Col(pHAD28). The main source of Salmonella enterica is the maternity areas, where periparturient shedders are contaminants and perpetuate the pathogen within the dairy in manure, sand, and concrete surfaces. This study demonstrated the necessity of implementing One Health control actions to diminish the prevalence of antimicrobial resistant and virulent pathogens including Salmonella.

Antibiotic Resistance Profiles and Molecular Characteristics of blaCMY-2-Carrying Salmonella enterica Serovar Albany Isolated from Chickens During 2013-2020 in South Korea

The production of β-lactamase by nontyphoidal Salmonella has become a public health issue throughout the world. In this study, we aimed to investigate the antimicrobial resistance profiles and molecular characteristics of β-lactamase-producing Salmonella enterica serovar Albany isolates. A total of 434 Salmonella Albany were obtained from feces and carcasses of healthy and diseased food-producing animals [cattle (n = 2), pigs (n = 3), chickens (n = 391), and ducks (n = 38)] during 2013-2020. Among the 434 Salmonella Albany isolates, 3.7% showed resistance to cefoxitin, and all the cefoxitin-resistant isolates were obtained from chickens. Moreover, Salmonella Albany isolates demonstrated high resistance to nalidixic acid (99.3%), trimethoprim/sulfamethoxazole (97.9%), ampicillin (86.6%), chloramphenicol (86.6%), and tetracycline (85.7%), as well as higher rates of multidrug resistance were detected in cefoxitin-resistant isolates compared to cefoxitin-susceptible isolates. All cefoxitin-resistant isolates harbored CMY-2-type β-lactamase and belonged to seven different pulsotypes, with type IV-b (43.75%) and IV-a (25%) making up the majority. In addition, genes encoding cefoxitin resistant of all blaCMY-2-harboring Salmonella Albany isolates were horizontally transmitted to a recipient Escherichia coli J53 by conjugation. Furthermore, 93.75% (15/16) of conjugative plasmids harboring blaCMY-2 genes belong to ST12/CC12-IncI1. Genetic characteristics of transmitted blaCMY-2 genes were associated with ISEcp1, which can play an essential role in the effective mobilization and expression of these genes. Salmonella Albany containing blaCMY-2 in chickens can potentially be transferred to humans. Therefore, it is necessary to restrict antibiotic use and conduct continuous monitoring and analysis of resistant bacteria in the poultry industry.

Invasive and Non-Invasive Human Salmonellosis Cases Admitted between 2015 and 2021 in Four Suburban Hospitals in the Metropolitan Area of Milan (Italy): A Multi-Center Retrospective Study

Non-Typhoidal Salmonellas (NTSs) are diffused worldwide. In Italy, more than 3500 cases are notified each year, but despite this, data about salmonellosis are scarce. Our multi-center, retrospective, descriptive study selected 252 patients with positive cultures for Salmonella spp. (feces 79.8%, blood 8.7%, feces and blood 7.5%), aiming to describe the epidemiological and clinical characteristics of this population. Bacteremic infections constituted 16.3% (41/252) of patients. Extreme ages (≤12 and ≥65 years old) accounted for 79.7%, but only elder ages were strongly associated with bacteremic infections (aOR 5.78). Invasive infections had a 7-fold higher mortality rate than non-invasive disease (9.8% vs. 1.4%, p = 0.013), with an overall rate of 2.8%. The two more represented serogroups were O:4 (52.8%) and O:9 (22.2%). The O:9 serogroup was strongly associated with a higher frequency of invasive infection (aOR 2.96, 95% CI 1.17-7.63). In particular, S. napoli, an emerging serovar in Europe, accounted for 31.7% of bacteremic infections and only 9.5% of non-bacteremic ones (p < 0.001). Antibiotic microbial resistance (AMR) observed a steep increasing trend and was detected in 60.4% of cases (122/202): amoxicillin/clavulanate, ampicillin, and gentamicin were most commonly involved (26.7%, 21.8%, 14.3%, respectively), while TMP/SMX, ciprofloxacin, and ceftriaxone were <10%. Resistance was, in general, less common in the O:9 serogroup, while amikacin resistance was significantly more common. Factors associated with an MDR Salmonella acquisition were time (OR 1.37 per year more), O:4 serogroup (OR 2.67), and being a woman (OR 2.11). The most frequent symptoms were diarrhea (90.5%) and fever (81.7%). In conclusion, our study highlights a high burden of NTS infections, leading to severe or fatal outcomes in frail patients. Furthermore, AMR shows an increasing trend with a concerning high prevalence of cephalosporine resistance compared to the rest of Europe.

Characteristics of Two mcr-1-Harboring IncHI2 Plasmids from Clinical Salmonella Isolates in Jiaxing City

Salmonella is a primary cause of foodborne diseases, and the increasing prevalence of mcr-1-carrying plasmids, which confer colistin resistance to Salmonella, poses significant global health concerns. As the frequency of occurrence of the mcr-1 gene is increasing globally, we studied the prevalence of mcr-1 in clinical Salmonella isolates by analyzing 195 clinical strains isolated in 2020. Of the 195 Salmonella isolates, 41 isolates were resistant to colistin. We found mcr-1 in two strains (Salmonella Typhimurium ZJJX20006 and Salmonella Kentucky ZJJX20014), which we analyzed in detail via whole-genome sequencing and antibiotic susceptibility testing. Two strains displayed resistance to ampicillin, ampicillin-sulbactam, tetracycline, chloramphenicol, and cotrimoxazole, while ZJJX20006 displayed resistance to colistin and ZJJX20014 was sensitive. Genomic analysis revealed that these strains had plasmid-encoded mcr-1 in IncHI2 plasmids, which were not similar to the mcr-1-IncX4 identified in 2016. These two strains also harbored other drug resistance genes, including blaOXA-1 and blaCTX-M-14. Our findings may help clarify the molecular mechanisms of mcr-1 dissemination among Salmonella strains in Jiaxing City and offer insights into the evolution of mcr-1 in Salmonella.

Persistence and dynamic structures of diverse cephalosporinase genes in nontyphoidal Salmonella in cross-sectional surveillance in Taiwan

OBJECTIVES

Nontyphoidal Salmonella (NTS) is a major foodborne pathogen causing from acute gastroenteritis to bacteraemia, particularly in paediatric and elderly patients. Antimicrobial resistance of NTS, especially resistance to extended-spectrum cephalosporins, has emerged over the past decades.

METHODS

Thirteen NTS isolates resistant to ceftriaxone or cefotaxime were collected from a teaching hospital in Taipei, and another three from a tertiary hospital, in New Taipei City, Taiwan, from September 2018 to December 2019. Ten other archived isolates from 2000 to 2017 were also obtained. Complete genomes of the 26 isolates were obtained. Serovars, sequence types, resistomes, genetic relatedness, and sequence comparison of plasmids were analyzed.

RESULTS

Serogroups B, C2 and E were significantly associated with ampicillin resistance. Over 90% of these 26 isolates are susceptible to carbapenems and colistin. Genomic epidemiology of these isolates shows that blaCMY-2-harbouring isolates in different serovars were prevalent over two decades, presumably resulting from highly mobile IncI1 plasmid harbouring blaCMY-2. One type of the IncI1 plasmids contained a mobile element, IS26, which might be involved in the acquisition of antimicrobial resistance genes. Two emerging serovars, S. Goldcoast ST358 harbouring blaCTX-M-55 on IncHI2 plasmids and S. Anatum ST64 harbouring blaDHA-1 on IncA/C2 plasmids persisted in Taiwan, possibly through the clonal spread. Integration of complete or partial plasmid sequences into host chromosomes or multiplications of the antimicrobial resistance genes also appears to be mediated by IS26, in the two emerging clones.

CONCLUSION

The dynamic movement of cephalosporinase genes mediated by IS26 in NTS is of great concern.

Efficacy of Different Encapsulation Techniques on the Viability and Stability of Diverse Phage under Simulated Gastric Conditions

Salmonella causes a range of diseases in humans and livestock of considerable public health and economic importance. Widespread antimicrobial use, particularly in intensively produced livestock (e.g., poultry and pigs) may contribute to the rise of multidrug-resistant Salmonella strains. Alternative treatments such as bacteriophages have shown promise when used to reduce the intestinal carriage of Salmonella in livestock. However, the digestive enzymes and low pH encountered in the monogastric GI tract can significantly reduce phage viability and impact therapeutic outcomes. This study deployed alginate-carrageenan microcapsules with and without CaCO3 to protect a genomically diverse set of five Salmonella bacteriophages from simulated gastrointestinal conditions. None of the unprotected phage could be recovered following exposure to pH < 3 for 10 min. Alginate-carrageenan encapsulation improved phage viability at pH 2-2.5 after exposure for 10 min, but not at pH 2 after 1 h. Including 1% (w/v) CaCO3 in the formulation further reduced phage loss to <0.5 log10 PFU/mL, even after 1 h at pH 2. In all cases, phage were efficiently released from the microcapsules following a shift to a neutral pH (7.5), simulating passage to the duodenum. In summary, alginate-carrageenan-CaCO3 encapsulation is a promising approach for targeted intestinal delivery of genomically diverse Salmonella bacteriophages.

A culture-based assessment of the microbiota of conventional and free-range chicken meat from Irish processing facilities

Chicken meat is the most popularly consumed meat worldwide, with free-range and ethically produced meat a growing market among consumers. However, poultry is frequently contaminated with spoilage microbes and zoonotic pathogens which impact the shelf-life and safety of the raw product, constituting a health risk to consumers. The free-range broiler microbiota is subject to various influences during rearing such as direct exposure to the external environment and wildlife which are not experienced during conventional rearing practices. Using culture-based microbiology approaches, this study aimed to determine whether there is a detectable difference in the microbiota from conventional and free-range broilers from selected Irish processing plants. This was done through analysis of the microbiological status of bone-in chicken thighs over the duration of the meat shelf-life. It was found that the shelf-life of these products was 10 days from arrival in the laboratory, with no statistically significant difference (P > 0.05) evident between free-range and conventionally raised chicken meat. A significant difference, however, was established in the presence of pathogenesis-associated genera in different meat processors. These results reinforce past findings which indicate that the processing environment and storage during shelf-life are key determinants of the microflora of chicken products reaching the consumer.

The rare Salmonella enterica serovar Isangi: genomic characterization of the antimicrobial resistance, virulence potential and epidemiology of Brazilian strains in comparison to global isolates

Introduction. Salmonella enterica serovar Isangi (S. Isangi) is a rare non-typhoidal serovar, related to invasive nosocomial infections in various countries and to increasing antimicrobial resistance rates.Gap statement. Despite existing reports on S. Isangi, there is a lack of information of specific traits regarding this serovar, which could be improved through genomic analyses.Aim. Our goals were to characterize the antimicrobial resistance, virulence potential and genomic relatedness of 11 S. Isangi strains from Brazil in comparison to 185 genomes of global isolates using whole-genome sequencing (WGS) data.Methodology. Phenotypic resistance was determined by disc-diffusion. The search for resistance genes, plasmids, prophages, Salmonella pathogenicity islands (SPIs) and virulence genes, plus multi-locus sequence typing (MLST) and core-genome MLST (cgMLST) were performed using WGS.Results. Brazilian S. Isangi strains showed phenotypic resistance to nalidixic acid, ciprofloxacin and streptomycin, and harboured antimicrobial resistance [qnrB19, aac(6')-Iaa, mdsAB] and heavy metal tolerance (arsD, golST) genes. Col(pHAD28) and IncFII(S) plasmids, virulence genes related to adherence, macrophage induction, magnesium uptake, regulation and type III secretion systems, 12 SPIs and eight prophages were detected. The 185 additional global genomes analysed harboured resistance genes against 11 classes of antimicrobial compounds, 22 types of plasmids, 32 prophages, 14 SPIs, and additional virulence genes related to serum resistance, stress adaptation and toxins. Sequence type (ST)216 was assigned to genomes from Brazil and other countries, while ST335 was the most frequent ST, especially among South African genomes. cgMLST showed that Brazilian genomes were more closely related to genomes from European and African countries, the USA and Taiwan, while the majority of South African genomes were more closely related among each other.Conclusion. The presence of S. Isangi strains from Brazil and different countries showing a close genomic correlation, antimicrobial resistance profiles to drugs used in human therapy and a large number of virulence determinants reinforced the need for stronger initiatives to monitor rare non-typhoidal Salmonella serovars such as S. Isangi in order to prevent its dissemination among human and non-human sources.

Genomic analysis of Anderson typing phages of Salmonella Typhimrium: towards understanding the basis of bacteria-phage interaction

The Anderson phage typing scheme has been successfully used worldwide for epidemiological surveillance of Salmonella enterica serovar Typhimurium. Although the scheme is being replaced by whole genome sequence subtyping methods, it can provide a valuable model system for study of phage-host interaction. The phage typing scheme distinguishes more than 300 definitive types of Salmonella Typhimurium based on their patterns of lysis to a unique collection of 30 specific Salmonella phages. In this study, we sequenced the genomes of 28 Anderson typing phages of Salmonella Typhimurium to begin to characterize the genetic determinants that are responsible for the differences in these phage type profiles. Genomic analysis of typing phages reveals that Anderson phages can be classified into three different groups, the P22-like, ES18-like and SETP3-like clusters. Most Anderson phages are short tailed P22-like viruses (genus Lederbergvirus); but phages STMP8 and STMP18 are very closely related to the lambdoid long tailed phage ES18, and phages STMP12 and STMP13 are related to the long noncontractile tailed, virulent phage SETP3. Most of these typing phages have complex genome relationships, but interestingly, two phage pairs STMP5 and STMP16 as well as STMP12 and STMP13 differ by a single nucleotide. The former affects a P22-like protein involved in DNA passage through the periplasm during its injection, and the latter affects a gene whose function is unknown. Using the Anderson phage typing scheme would provide insights into phage biology and the development of phage therapy for the treatment of antibiotic resistant bacterial infections.

Integrative and Conjugative Element-Mediated Azithromycin Resistance in Multidrug-Resistant Salmonella enterica serovar Albany

We identified an erm42-carrying integrative and conjugative element, ICE_erm42, in 26.4% of multidrug-resistant Salmonella enterica serovar Albany isolates recovered from human salmonellosis between 2014 and 2019 in Taiwan. ICE_erm42-carrying strains displayed high-level resistance to azithromycin and the element could move into the phylogenetically distant Vibrio cholerae via conjugation.

Isolation, susceptibility profiles and genomic analysis of a colistin-resistant Salmonella enterica serovar Kentucky strain COL-R

Salmonella enterica serovar Kentucky is a frequent cause for clinical infections in human patients. They are isolated and reported with multidrug resistance from the foods of animal origin from various countries. However, studies inferring the colistin resistance are limited. Hence, the current study reports the genetic factors and genomic analysis of the colistin-resistant Salmonella enterica serovar Kentucky strain COL-R for better understanding of its pathogenic potential and phylogenetic relatedness. The S. Kentucky strain COL-R was successfully isolated from chicken meat during ongoing surveillance of food of animal origin. Antimicrobial susceptibility testing revealed resistance to cefoxitin, erythromycin, gentamicin, tetracycline, and most disturbingly to ciprofloxacin and colistin (broth microdilution method). Whole-genome sequence of the COL-R strain was subjected to various in silico analysis to identify the virulence factors, antimicrobial resistance genes, pathogenicity islands and sequence type. The S. Kentucky COL-R strain belonged to sequence type (ST) 198 with a high probability (0.943) of being a human pathogen. Besides presence of integrated phage in the S. Kentucky COL-R genome, 38 genes conferring resistance to various antimicrobials and disinfectants were also identified. Nucleotide Polymorphism analysis indicated triple mutations in gyrA and parC genes conferring fluoroquinolone resistance. Phylogenomic analysis with 31 other S. Kentucky genomes revealed discernible clusters with S. Kentucky COL-R strain latching onto a cluster of high diversity (geographic location and isolation sources). Taken together, our results document the first occurrence of colistin resistance in a fluoroquinolone resistant S. Kentucky COL-R strain isolated from retail chicken and provide crucial information on the genomic features of the strain.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03559-2.

Genomic analyses of drug-resistant Salmonella enterica serovar Heidelberg strains isolated from meat and related sources between 2013 and 2017 in the south region of Brazil

Salmonella enterica serovar Heidelberg (S. Heidelberg) is a zoonotic, ubiquitous, and worldwide-distributed pathogen, responsible for gastroenteritis in humans caused by the consumption of contaminated food. In this study, 11 S. Heidelberg strains isolated from chicken and bovine meat, drag swab, and animal feed between 2013 and 2017 in states of the southern region of Brazil were characterized by whole-genome sequencing (WGS) analyses. Antimicrobial resistance against 18 antimicrobials was determined by disk-diffusion and ciprofloxacin's minimum inhibitory concentration by Etest®. The search for resistance and virulence genes, plasmids, Salmonella Pathogenicity Islands (SPIs) plus multi-locus sequence typing (MLST), and single-nucleotide polymorphisms (SNPs) analyses was conducted using WGS data. All strains harbored resistance genes fosA7, aac(6')-Iaa, sul2, tet(A), bla_CMY-2, mdsA, and mdsB_, and point mutations in gyrA and parC. All strains showed a phenotypic multidrug-resistant profile, with resistant or intermediate resistant profiles against 14 antimicrobials tested. Plasmids ColpVC, IncC, IncX1, and IncI1-I(Alpha) were detected. Virulence genes related to adherence, macrophage induction, magnesium uptake, regulation, and type III secretion systems plus 10 SPIs were detected. All strains were assigned to ST15 and belonged to two SNP clusters showing high similarity to isolates from the United Kingdom, Chile, Germany, the Netherlands, China, South Africa, and South Korea. In conclusion, the presence of multidrug-resistant S. Heidelberg strains in Brazil showing a global genomic relationship may alert for the necessity of stronger surveillance measures by food safety and public health authorities to limit its spread to humans and animals through foods.

Whole-Genome Analysis of Antimicrobial-Resistant Salmonella enterica Isolated from Duck Carcasses in Hanoi, Vietnam

Salmonella enterica is one of the most dangerous foodborne pathogens listed by the World Health Organization. In this study, whole-duck samples were collected at wet markets in five districts in Hanoi, Vietnam, in October 2019 to assess their Salmonella infection rates and evaluate the susceptibility of the isolated strains to antibiotics currently used in the prophylaxis and treatment of Salmonella infection. Based on the antibiotic resistance profiles, eight multidrug resistance strains were whole-genome-sequenced, and their antibiotic resistance genes, genotypes, multi-locus sequence-based typing (MLST), virulence factors, and plasmids were analyzed. The results of the antibiotic susceptibility test indicate that phenotypic resistance to tetracycline and cefazolin was the most common (82.4%, 28/34 samples). However, all isolates were susceptible to cefoxitin and meropenem. Among the eight sequenced strains, we identified 43 genes associated with resistance to multiple classes of antibiotics such as aminoglycoside, beta-lactam, chloramphenicol, lincosamide, quinolone, and tetracycline. Notably, all strains carried the blaCTX-M-55 gene, which confers resistance to third-generation antibiotics including cefotaxime, cefoperazone, ceftizoxime, and ceftazidime, as well as resistance genes of other broad-spectrum antibiotics used in clinical treatment such as gentamicin, tetracycline, chloramphenicol, and ampicillin. Forty-three different antibiotic resistance genes were predicted to be present in the isolated Salmonella strains’ genomes. In addition, three plasmids were predicted in two strains, 43_S11 and 60_S17. The sequenced genomes also indicated that all strains carried SPI-1, SPI-2, and SPI-3. These SPIs are composed of antimicrobial resistance gene clusters and thus represent a potential threat to public health management. Taken together, this study highlights the extent of multidrug-resistant Salmonella contamination in duck meat in Vietnam.

Antimicrobial Resistance and Mechanisms of Azithromycin Resistance in Nontyphoidal Salmonella Isolates in Taiwan, 2017 to 2018

Antimicrobial resistance was investigated in 2,341 nontyphoidal Salmonella (NTS) isolates recovered from humans in Taiwan from 2017 to 2018 using antimicrobial susceptibility testing. Azithromycin resistance determinants were detected in 175 selected isolates using PCR and confirmed in 81 selected isolates using whole-genome sequencing. Multidrug resistance was found in 47.3% of total isolates and 96.2% of Salmonella enterica serovar Anatum and 81.7% of S. enterica serovar Typhimurium isolates. Resistance to the conventional first-line drugs (ampicillin, chloramphenicol, and cotrimoxazole), cefotaxime and ceftazidime, and ciprofloxacin was found in 32.5 to 49.0%, 20.3 to 20.4%, and 3.2% of isolates, respectively. A total of 76 (3.1%) isolates were resistant to azithromycin, which was associated with mph(A), erm(42), erm(B), and possibly the enhanced expression of efflux pump(s) due to ramAp or defective ramR. mph(A) was found in 53% of the 76 azithromycin-resistant isolates from 11 serovars and located in an IS26-mph(A)-mrx(A)-mphR(A)-IS6100 unit in various incompatibility plasmids and the chromosomes. erm(42) in S. enterica serovar Albany was carried by an integrative and conjugative element, ICE_erm42, and in S. enterica serovar Enteritidis and S. Typhimurium was located in IS26 composite transposons in the chromosomes. erm(B) was carried by IncI1-I(α) plasmids in S. Enteritidis and S. Typhimurium. ramAp was a plasmid-borne ramA, a regulatory activator of efflux pump(s), found in only S. enterica serovar Goldcoast. Since the azithromycin resistance determinants are primarily carried on mobile genetic elements, they could easily be disseminated among human bacterial pathogens. The ramAp-carrying S. Goldcoast isolates displayed azithromycin MICs of 16 to 32 mg/L. Thus, the epidemiological cutoff value of ≤16 mg/L of azithromycin proposed for wild-type NTS should be reconsidered. IMPORTANCE Antimicrobial resistance in NTS isolates is a major public health concern in Taiwan, and the mechanisms of azithromycin resistance are rarely investigated. Azithromycin and carbapenems are the last resort for the treatment of invasive salmonellosis caused by multidrug-resistant (MDR) and extensively drug-resistant Salmonella strains. Our study reports the epidemiological trend of resistance in NTS in Taiwan and the genetic determinants involved in azithromycin resistance. We point out that nearly half of NTS isolates from 2017 to 2018 are MDR, and 20% are resistant to third-generation cephalosporins. The azithromycin resistance rate (3.1%) for the NTS isolates from Taiwan is much higher than those for the NTS isolates from the United States and Europe. Our study also indicates that azithromycin resistance is primarily mediated by mph(A), erm(42), erm(B), and ramAp, which are frequently carried on mobile genetic elements. Thus, the azithromycin resistance determinants could be expected to be disseminated among diverse bacterial pathogens.

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.

Plasmid Composition, Antimicrobial Resistance and Virulence Genes Profiles of Ciprofloxacin- and Third-Generation Cephalosporin-Resistant Foodborne Salmonella enterica Isolates from Russia

Salmonella enterica is an important foodborne pathogen worldwide. Ciprofloxacin and extended-spectrum cephalosporins are the common first-line antimicrobial drugs for the treatment of salmonellosis, antimicrobial resistance genes for which are mostly transferred via plasmids. The goal of this work was to perform genomic analysis of plasmids from foodborne S. enterica isolates obtained in Russia based on whole-genome sequencing. In the current study, 11 multidrug-resistant samples isolated in 2021 from 8 regions of Russia were selected based on their resistance to ciprofloxacin and third-generation cephalosporins (CIP-3rd). Whole-genome short-read sequencing (WGS) was performed for all isolates; the samples belonged to five different sequence types (ST32, ST469, ST11, ST142, and ST548) which had different profiles of antimicrobial resistance (AMR) and virulence genes. We have performed additional long-read sequencing of four representative S. enterica isolates, which showed that they carried pESI-like megaplasmids of 202-280 kb length harboring extended-spectrum β-lactamase genes, fluoroquinolone, tetracycline, and aminoglycosides resistance genes, as well as several virulence determinants. We believe that the WGS data obtained will greatly facilitate further studies of foodborne S. enterica isolates epidemiology in terms of their self-transmissible plasmid composition that mediated antimicrobial resistance and virulence determinants conferring selective advantages of this important bacterial pathogen.

Geography shapes the genomics and antimicrobial resistance of Salmonella enterica Serovar Enteritidis isolated from humans

Multidrug-resistant (MDR) Salmonella has been a long-standing challenge in public health and food safety. The prevalence of MDR S. Enteritidis, especially isolated from humans, in China is significantly higher than those from the U.S. and other countries. A dataset of 197 S. Enteritidis genomes, including 16 sequenced clinical isolates from China and 181 downloaded genomes of human isolates from the U.S., Europe, and Africa, was analyzed for genomic diversity, virulence potential, and antimicrobial resistance (AMR). Phylogenomic analyses identified four major well-supported clades (I-IV). While AMR genotype in the majority of isolates in clades I and IV displayed as pan-susceptible, 81.8% (9/11) and 22.4% (13/58) of isolates in clades III and II were MDR, respectively. It is noted that 77% (10/13) of MDR isolates in clade II were from China. The most common antimicrobial resistance genes (ARGs) carried by the Chinese isolates were aph(3')-IIa, bla_CTX-M-55, and bla_TEM-1B, whereas bla_TEM-1B, sul1, sul2, drfA7, aph(3")-Ib/strA, and aph(6)-Id/strB were most often identified in those from Africa (clade III). Among the 14 plasmid types identified, IncX1 and IncFII(pHN7A8) were found exclusively in the Chinese MDR isolates, while IncQ1 was highly associated with the African MDR isolates. The spvRABCD virulence operon was present in 94.9% (187/197) of isolates tested and was highly associated with both the IncF (IncFII and IncFIB) plasmids. In addition, phylogenetic differences in distribution of Salmonella pathogenicity islands (SPIs), prophages and other accessory genes were also noted. Taken together, these findings provide new insights into the molecular mechanisms underpinning diversification of MDR S. Enteritidis.

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.

Genomic characterization of Salmonella enterica serovar Choleraesuis from Brazil reveals a swine gallbladder isolate harboring colistin resistance gene mcr-1.1

Salmonella enterica serovar Choleraesuis (S. Choleraesuis) is a swine-adapted serovar associated to invasive infections in humans. In Brazil, data of strains of this serovar are scarce. In the present study, six S. Choleraesuis strains of animal (n = 5) and human (n = 1) origin from Brazil were screened for phenotypic antimicrobial resistance using disk-diffusion assay and using whole-genome sequencing data to search for antimicrobial resistance genes, plasmids, prophages, and Salmonella pathogenicity islands (SPIs). Its genetic relatedness was evaluated by MLST and SNP analysis. A single isolate from swine gallbladder harbored the colistin resistance gene mcr-1.1 into a IncX4 plasmid. In the six strains analyzed, resistance was found to tetracycline, nalidixic acid, ciprofloxacin, ampicillin, piperacillin, streptomycin, cefazoline, gentamycin, sulfamethoxazole-trimethoprim, and choloramphenicol, along with resistance genes aac(6')-Iaa, aac(3)-IV, aph(3'')-Ib, aph(6)-Id, aph(4)-Ia, aadA1, aph(3')-IIa, blaTEM-1A, floR, sul1, sul2, tet(B), drfA1, erm(B), mph(B), lnu(G), qacE, and gyrA point mutation Serine83 → Tyrosine and parC Threonine57 → Serine. Furthermore, IncF and IncH plasmids, ten SPIs, and seven prophage types were detected. All strains were assigned to ST145 and five belonged to a common SNP cluster of S. Choleraesuis strains from Brazil. The presence of S. Choleraesuis isolated from animals harboring relevant antimicrobial resistance profiles and virulence determinants reinforced the urge for enhanced surveillance to avoid its transmission to humans through food items.

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.

Discovery of antipsychotic loxapine derivatives against intracellular multidrug-resistant bacteria

The emergence and spread of multidrug-resistant bacteria highlight the need for new antibacterial interventions. A screening of 24 newly synthesized dibenzoxazepines identified a small molecule compound, SW14, with potent inhibitory activity against intracellular multidrug-resistant and fluoroquinolone-resistant strains of S. typhimurium in macrophages and epithelial cells. Moreover, intra-macrophagic Salmonella typhi, Yersinia enterocolitica, and Listeria monocytogenes and methicillin-resistant Staphylococcus aureus are also susceptible to SW14. Overall, our findings suggest that SW14 has a broad-spectrum activity against intracellular bacteria.

Antibiotic Resistance Profiles and Molecular Characteristics of blaCTX-M-15-Carrying Salmonella enterica Serovar Enteritidis Isolates from Healthy and Diseased Chickens in Korea

Extended-spectrum β-lactamase (ESBL)-producing Salmonella enterica serovar Enteritidis has emerged as a public health concern. The main objectives of this study were therefore to determine the antimicrobial susceptibility profiles of Salmonella Enteritidis and to investigate the molecular characteristics of identified ESBL-producing isolates. In the study, 237 Salmonella Enteritidis isolates (232 isolates from chickens, 4 from cattle, and 1 from a pig) were recovered from carcasses and fecal samples of healthy and diseased food animals between 2010 and 2017. Ceftiofur resistance was noted only in chicken isolates (43%, 102/237), with the highest in healthy chickens and their carcasses (48.3%, 83/172) compared with that in diseased chickens (31.7%, 19/60). All of the ceftiofur-resistant isolates exhibited resistance to multiple antimicrobials. Indeed, a relatively higher percentage of ceftiofur-resistant isolates demonstrated resistance to the tested aminoglycosides and tetracycline compared with the ceftiofur-susceptible strains. In this study, bla_CTX-M-15 was the only ESBL gene detected in all of the ceftiofur-resistant isolates. The bla_CTX-M-15-carrying isolates belonged to 11 different pulsotypes. The bla_CTX-M-15 gene was transferred from 20.6% (21/102) of the bla_CTX-M-15-harboring isolates to a recipient Escherichia coli J53. The coexistence of IncHI2/ST2 and IncFIIs/ST1 plasmids was noted in the majority (81.8%, 18/22) of the transconjugants. E. coli J53 transconjugants carrying bla_CTX-M-15 gene showed distinct genetic environments, predominantly ISEcp1-bla_CTX-M-15-orf477 (15/21, 71.4%). This study demonstrated that healthy chickens and their carcasses act as reservoirs of bla_CTX-M-15-carrying Salmonella Enteritidis that can potentially be transmitted to humans.

First Report on Abortion Caused by Salmonella enterica subsp. enterica Serovar Enteritidis in Water Buffalo (Bubalus bubalis)

Salmonella enterica subsp. enterica Serovar Enteritidis is one of the major pathogens associated with enteric diseases in animals and humans. Thus, due to the importance of Salmonella spp. infections for animal production and public health, the aim of the present study was to describe the first detection of S. enteritidis in an aborted water buffalo fetus in southern Italy by characterizing the phylogroup profile and the antimicrobial susceptibility of the isolated pathogenic strains. The different clinical manifestations of salmonellosis in animals include diarrhea, abortion, pneumonia, septic arthritis, meningitis, and others, depending on the virulence of the serovars, infectious dose, and host immunity. This study reports the first case of abortion caused by Salmonella enterica subsp enterica serovar Enteritidis in water buffalo (Bubalus bubalis) in the Campania region, southern Italy. Complete necropsy was performed on the aborted water buffalo fetus under study, and samples and swabs from different organs were collected. Samples were processed by microbiological and molecular analyses to detect bacterial, viral, and protozoarian pathogens possibly responsible for abortion. Whole genome sequencing (WGS) was carried out to further characterize the isolated S. Enteritidis strain. Our findings highlight the crucial role of S. Enteritidis as a potential abortive agent in water buffalo and its presence should therefore be investigated in cases of bubaline abortion.

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.

Clinical data from studies involving novel antibiotics to treat multidrug-resistant Gram-negative bacterial infections

Multidrug-resistant (MDR) Gram-negative bacteria (GNB) are a critical threat to healthcare worldwide, worsening outcomes and increasing mortality among infected patients. Carbapenemase- and extended-spectrum β-lactamase-producing Enterobacterales, as well as carbapenemase-producing Pseudomonas and Acinetobacter spp., are common MDR pathogens. To address this threat, new antibiotics and combinations have been developed. Clinical trial findings support several combinations, notably ceftazidime-avibactam (CZA, a cephalosporin-β-lactamase inhibitor combination) which is effective in treating complicated urinary tract infections (cUTI), complicated intra-abdominal infections and hospital-acquired and ventilator-associated pneumonia caused by GNBs. Other clinically effective combinations include meropenem-vaborbactam (MVB), ceftolozane-tazobactam (C/T) and imipenem- relebactam (I-R). Cefiderocol is a recent siderophore β-lactam antibiotic that is useful against cUTIs caused by carbapenem-resistant Enterobacterales (CRE) and is stable against many β-lactamases. CRE are a genetically heterogeneous group that vary in different world regions and are a substantial cause of infections, among which Klebsiella pneumoniae are the most common. Susceptible CRE infections can be treated with fluoroquinolones, aminoglycosides or fosfomycin, but alternatives include CZA, MVB, I-R, cefiderocol, tigecycline and eravacycline. MDR Acinetobacter baumannii and Pseudomonas aeruginosa are increasingly common pathogens producing a range of different carbapenemases, and infections are challenging to treat, often requiring novel antibiotics or combinations. Currently, no single agent can treat all MDR-GNB infections, but new β-lactam-β-lactamase inhibitor combinations are often effective for different infection sites, and, when used appropriately, have the potential to improve outcomes. This article reviews clinical studies investigating novel β-lactam approaches for treatment of MDR-GNB infections.

Prevalence of Chromosomally Located blaCTX-M-55 in Salmonella Typhimurium ST34 Isolates Recovered from a Tertiary Hospital in Guangzhou, China

Nontyphoidal Salmonella (NTS) is one of the most prevalent bacterial causes of gastrointestinal infections worldwide. Meanwhile, the detection rate of CTX-M-55 ESBL-positive has increased gradually in China. To identify the molecular epidemiological and genomic characteristics of blaCTX-M-55-carrying nontyphoidal Salmonella (NTS) clinical isolates, a total of 105 NTS isolates were collected from a Chinese tertiary hospital. Antimicrobial susceptibility testing was performed to determine the resistance phenotype. Whole-genome sequencing and bioinformatics analysis were used to determine the antimicrobial resistance genes, serotypes, phylogenetic relationships, and the genetic environment of the blaCTX-M-55 gene. The results showed that among the 22 ceftriaxone resistant isolates, the blaCTX-M-55 was the most common β-Lactamase gene carried by 14 isolates, including serotypes S. Typhimurium (10/14), S. Muenster (2/14), S. Rissen (1/14), and S. Saintpaul (1/14). Phylogenetic analysis shows that 10 blaCTX-M-55-positive S. Typhimurium ST34 isolates were divided into two clusters. The genetic relationship of isolates in each cluster was very close (≤10 cgMLST loci). The blaCTX-M-55 gene was located on the chromosome in 10 isolates, on IncI1 plasmid in three isolates, and IncHI2 plasmid in one isolate. In conclusion, the blaCTX-M-55 gene, mainly located on the chromosome of S. Typhimurium ST34 isolates, was the main driving force associated with the resistance of NTS to cephalosporins. Therefore, close attention to the clonal dissemination of blaCTX-M-55-carrying S. Typhimurium ST34 in clinical settings must be monitored carefully. IMPORTANCE ESCs are the first choice for treating NTS infections. However, ESBLs and AmpC β-lactamases are the most typical cause for ESCs resistance. The CTX-M-55 ESBL-positive rate has gradually increased in the clinic in recent years. At present, the research about blaCTX-M-55-positive Salmonella mainly focuses on the foodborne animals or the environment while less on clinical patients. Thus, this study was carried out for identifying molecular epidemiological and genomic characteristics of blaCTX-M-55-carrying NTS clinical isolates. The results showed that the blaCTX-M-55 gene, mainly located on the chromosome of S. Typhimurium ST34 isolates from Conghua District, was the main driving force associated with the resistance of NTS to cephalosporins. Therefore, our work highlights the importance of monitoring the clonal dissemination of blaCTX-M-55-carrying S. Typhimurium ST34 in clinical settings.

Whole Genome Sequencing, Antibiotic Resistance, and Epidemiology Features of Nontyphoidal Salmonella Isolated From Diarrheic Children: Evidence From North China

Nontyphoidal Salmonella (NTS) in children remains a growing burden on public health and often causes children to be hospitalized with diarrheic symptoms. In this work, 260 strains of human Salmonella isolated from Jilin, China were characterized by serotypes and antimicrobial resistance using whole genome sequencing (WGS). The most prevalent serotype was Salmonella enteritidis (47.3%), followed by S. I 4,[5],12:i:- (33.1%), and Salmonella Typhimurium (7.3%). Furthermore, the consistency between resistance phenotype and genotype was confirmed. Similarly, strains harbored bla_TEM−1B and tetA genes were detected, which verified the level of resistant phenotype in β-lactams and tetracyclines. The presence of a single mutation in parC, gyrA, and qnrS1 genes corresponding to quinolones was also observed. In our work, multilocus sequence typing (MLST) and core genome multilocus sequence typing (cgMLST) were found to have a high resolution to molecular traceability, and the combination of both was conducive to practical application in an actual situation. Taking all of this into account, we suggested that the comprehensive surveillance of Salmonella infection in children should be carried out to monitor antimicrobial-resistant trends from various sources and to alert on outbreaks of foodborne diseases to protect public health.

Efficacy of a Biocidal Paint in Controlling Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae) and Improving the Quality of Air and Litter in Poultry Houses

Effective disinfection and disinsection are the keys to successful operation of modern poultry farms and the safety of poultry products. The cleaning and disinfection of poultry houses are important aspects of farm hygiene management. The correct execution of all steps of cleaning, disinfection, and disinsection procedures and the use of appropriate products are crucial for the prevention and control of zoonotic and animal diseases. In this study it was assumed that a water-based slow-release biocidal paint could be useful in controlling insect pests such as Alphitobius diaperinus and reducing microbiological contamination of air and litter in poultry houses and have a beneficial effect on microclimate in poultry houses. Therefore, the locations of A. diaperinus in the poultry houses, the microbiological contamination of air and litter, as well as the microclimatic conditions in the houses and the physicochemical parameters of the litter were evaluated. The results suggest that the tested biocidal paint could be an effective alternative to other insecticides and disinfectants. Additionally, the research is of a practical nature and may be very useful for poultry producers in controlling A. diaperinus populations and maintaining proper hygiene in poultry houses. Further research is needed.

Research progress on antibiotic resistance of Salmonella

Antibiotic abuse results in various antibiotic resistance among a number of foodborne bacteria, posing a severe threat to food safety. Antibiotic resistance genes are commonly detected in foodborne pathogens, which has sparked much interest in finding solutions to these issues. Various strategies against these drug-resistant pathogens have been studied, including new antibiotics and phages. Recently, a powerful tool has been introduced in the fight against drug-resistant pathogens, namely, clustered regularly interspaced short palindromic repeats-CRISPR associated (CRISPR-Cas) system aggregated by a prokaryotic defense mechanism. This review summarized the mechanism of antibiotic resistance in Salmonella and resistance to common antibiotics, analysed the relationship between Salmonella CRISPR-Cas and antibiotic resistance, discussed the changes in antibiotic resistance on the structure and function of CRISPR-Cas, and finally predicted the mechanism of CRISPR-Cas intervention in Salmonella antibiotic resistance. In the future, CRISPR-Cas is expected to become an important tool to reduce the threat of antibiotic-resistant pathogens in food safety.

Draft Whole-Genome Sequences of Two Multidrug-Resistant Salmonella enterica Serovar Senftenberg Sequence Type 14 Strains Resistant to Ciprofloxacin, Ceftriaxone, and/or Azithromycin, Isolated from Kolkata, India

We report draft whole-genome sequences of two multidrug-resistant Salmonella enterica serovar Senftenberg sequence type 14 strains resistant to ciprofloxacin, ceftriaxone, and/or azithromycin, which were isolated from neonatal stool and goat meat in Kolkata, India. The genome characteristics, as well as the antimicrobial resistance genes, plasmid types, and integrons, are presented in this report.

Genomic characterization and antimicrobial resistance profiles of Salmonella enterica serovar Infantis isolated from food, humans and veterinary-related sources in Brazil

AIMS

To characterize the genetic relatedness, phenotypic and genotypic antimicrobial resistance and plasmid content of 80 Salmonella Infantis strains isolated from food, humans and veterinary sources from 2013 to 2018 in Brazil.

METHODS AND RESULTS

Pulsed-field gel electrophoresis and single-nucleotide polymorphism analysis showed major clusters containing 50% and 38.8% of the strains studied respectively. Multilocus sequence typing assigned all strains to ST32. Disk-diffusion revealed that 90% of the strains presented resistant or intermediate resistant profiles and 38.8% displayed multidrug resistance. Resistance genes for aminoglycosides (aac(6')-Iaa; aadA12; aph(3″-Ib; aph(6)-Id), β-lactams (bla_TEM-1 ; bla_CTX-M-8 ; bla_CMY-2 ), trimethoprim (dfrA8), tetracycline (tet(A)), amphenicols (floR), sulfonamide (sul2), efflux pumps (mdsA; mdsB), chromosomal point mutations in gyrB, parC, acrB and pmrA were detected. Strains harboured IncI, IncF, IncX, IncQ, IncN and IncR plasmids.

CONCLUSIONS

The presence of a prevalent S. Infantis subtype in Brazil and the high antimicrobial resistance rates reinforced the potential hazard of this serovar for the public health and food safety fields.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study characterizing a large set of S. Infantis from Brazil by whole-genome sequencing, which provided a better local and global comprehension about the distribution and characteristics of this serovar of importance in the food, human and veterinary fields.

Genetic Characterization of Salmonella Infantis with Multiple Drug Resistance Profiles Isolated from a Poultry-Farm in Chile

Salmonella comprises over 2500 serotypes and foodborne contamination associated with this pathogen remains an important health concern worldwide. During the last decade, a shift in serotype prevalence has occurred as traditionally less prevalent serotypes are increasing in frequency of infections, especially those related to poultry meat contamination. S. Infantis is one of the major emerging serotypes, and these strains commonly display antimicrobial resistance and can persist despite cleaning protocols. Thus, this work aimed to isolate S. Infantis strains from a poultry meat farm in Santiago, Chile and to characterize genetic variations present in them. We determined their genomic and phenotypic profiles at different points along the production line. The results indicate that the strains encompass 853 polymorphic sites (core-SNPs) with isolates differing from one another by 0-347 core SNPs, suggesting variation among them; however, we found discrete correlations with the source of the sample in the production line. Furthermore, the pan-genome was composed of 4854 total gene clusters of which 2618 (53.9%) corresponds to the core-genome and only 181 (3.7%) are unique genes (those present in one particular strain). This preliminary analysis will enrich the surveillance of Salmonella, yet further studies are required to assess their evolution and phylogeny.

Multidrug Resistance Dynamics in Salmonella in Food Animals in the United States: An Analysis of Genomes from Public Databases

The number of bacterial genomes deposited each year in public databases is growing exponentially. However, efforts to use these genomes to track trends in antimicrobial resistance (AMR) have been limited thus far. We used 22,102 genomes from public databases to track AMR trends in nontyphoidal Salmonella in food animals in the United States. In 2018, genomes deposited in public databases carried genes conferring resistance, on average, to 2.08 antimicrobial classes in poultry, 1.74 in bovines, and 1.28 in swine. This represents a decline in AMR of over 70% compared to the levels in 2000 in bovines and swine, and an increase of 13% for poultry. Trends in resistance inferred from genomic data showed good agreement with U.S. phenotypic surveillance data (weighted mean absolute difference ± standard deviation, 5.86% ± 8.11%). In 2018, resistance to 3rd-generation cephalosporins in bovines, swine, and poultry decreased to 9.97% on average, whereas in quinolones and 4th-generation cephalosporins, resistance increased to 12.53% and 3.87%, respectively. This was concomitant with a decrease of bla_CMY-2 but an increase in bla_CTX-M-65 and gyrA D87Y (encoding a change of D to Y at position 87). Core genome single-nucleotide polymorphism (SNP) phylogenies show that resistance to these antimicrobial classes was predominantly associated with Salmonella enterica serovar Infantis and, to a lesser extent, S. enterica serovar Typhimurium and its monophasic variant I 4,[5],12:i:−, whereas quinolone resistance was also associated with S. enterica serovar Dublin. Between 2000 and 2018, trends in serovar prevalence showed a composition shift where S. Typhimurium decreased while S. Infantis increased. Our findings illustrate the growing potential of using genomes in public databases to track AMR in regions where sequencing capacities are currently expanding.

IMPORTANCE Next-generation sequencing has led to an exponential increase in the number of genomes deposited in public repositories. This growing volume of information presents opportunities to track the prevalence of genes conferring antimicrobial resistance (AMR), a growing threat to the health of humans and animals. Using 22,102 public genomes, we estimated that the prevalence of multidrug resistance (MDR) in the United States decreased in nontyphoidal Salmonella isolates recovered from bovines and swine between 2000 and 2018, whereas it increased in poultry. These trends are consistent with those detected by national surveillance systems that monitor resistance using phenotypic testing. However, using genomes, we identified that genes conferring resistance to critically important antimicrobials were associated with specific MDR serovars that could be the focus for future interventions. Our analysis illustrates the growing potential of public repositories to monitor AMR trends and shows that similar efforts could soon be carried out in other regions where genomic surveillance is increasing.

Antimicrobial resistance patterns, virulence gene profiles, and genetic diversity of Salmonella enterica serotype Enteritidis isolated from patients with gastroenteritis in various Iranian cities

Objectives

This study aimed to evaluate antibiotic resistance profiles and presence of virulence genes among Salmonella enterica serovar Enteritidis (S. Enteritidis) isolated from patients with gastroenteritis in various regions of Iran. Moreover, genetic relatedness among the strains was assessed by pulsed-field gel electrophoresis (PFGE).

Materials and Methods

From April through September 2017, 59 Salmonella strains were isolated from 2116 stool samples. Of these strains, 27 S. Enteritidis were recovered. These strains were subjected to disk diffusion tests, polymerase chain reaction (PCR) for detection of virulence genes (invA, hilA, pefA, rck, stn, ssrA, ssaR, sefA, spvC, sipA, sipC, sopB, sopE, and sopE2), and PFGE.

Results

High prevalence of resistance towards cefuroxime (n = 20, 74.1%) and ciprofloxacin (n = 13, 48.2%) were demonstrated. All tested strains possessed invA, hilA, sefA, sipA, sopB, and sopE. The least prevalent virulence gene was rck (n = 6; 22.2%). Based on combinations of virulence genes, 12 virulotypes were observed. The most common virulotype was VP2 (n = 12; 44.4%), harboring all of the virulence genes except for rck. PFGE typing showed only two distinct fingerprints among tested strains. Each fingerprint had completely different virulotypes. Notably, VP4 (harboring all genes except for rck and spvC) was only presented in pulsotype A, while VP2 was confined to pulsotype B.

Conclusion

S. Enteritidis strains were derived from a limited number of clones, suggesting that it is highly homogenous. Future works should consider combinations of other genotyping methods together with larger sample sizes from more diverse sources.

Presence of Tetracycline and Sulfonamide Resistance Genes in Salmonella spp.: Literature Review

Tetracyclines and sulfonamides are broad-spectrum antibacterial agents which have been used to treat bacterial infections for over half a century. The widespread use of tetracyclines and sulfonamides led to the emergence of resistance in a diverse group of bacteria. This resistance can be studied by searching for resistance genes present in the bacteria responsible for different resistance mechanisms. Salmonella is one of the leading bacteria causing foodborne diseases worldwide, and its resistance to tetracyclines and sulfonamides has been widely reported. The literature review searched the Virtual Health Library for articles with specific data in the studied samples: the resistance genes found, the primers used in PCR, and the thermocycler conditions. The results revealed that Salmonella presented high rates of resistance to tetracycline and sulfonamide, and the most frequent samples used to isolate Salmonella were poultry and pork. The tetracycline resistance genes most frequently detected from Salmonella spp. were tetA followed by tetB. The gene sul1 followed by sul2 were the most frequently sulfonamide resistance genes present in Salmonella. These genes are associated with plasmids, transposons, or both, and are often conjugative, highlighting the transference potential of these genes to other bacteria, environments, animals, and humans.

Systematic Review: Nontyphoidal Salmonella in Food from Latin America

In Latin America, nontyphoidal Salmonella (NTS) is one of the most important etiological agents of foodborne infections; it can survive in soil, water, and food even after processing. Here, we aimed to perform a systematic review by collecting data on the prevalence, serotypes, and antimicrobial resistance (AMR) of NTS isolated from different food products in Latin America, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Out of 1766 studies screened, 244 reports from 13 Latin American countries were eligible. Among these, 182 reported NTS prevalence, 87 reported NTS serotypes, and 83 reported serotypes with AMR patterns. The NTS prevalence ranged from 0.005% to 93.3%, regardless of country and food. Meat showed the highest NTS prevalence. Enteritidis, Typhimurium, and Derby were the most frequently observed serotypes in different food products. The serotypes Enteritidis, Typhimurium, and Infantis, isolated from animal products, showed the highest AMR rate. The presence of NTS in fruits and vegetables, which are generally consumed raw or as ready-to-eat food, indicates a high risk of salmonellosis from consuming these foods. Thus, the reduction of this pathogen in the food chain requires a One Health approach, involving good agricultural and manufacturing practices, low antimicrobial use, and proper waste management.

Antibiotic Resistance and Plasmid Profile Analysis of Salmonella Enteritidis Isolated in Siberia and the Far East of Russia between 1990 and 2017

Salmonella is one of the major causes of foodborne disease outbreaks globally. Specifically, Salmonella enterica subsp. enterica serovar Enteritidis (S. Enteritidis) is one of the major causes of zoonotic Salmonella infection in humans worldwide. In this study, we present data on antimicrobial resistance (AMR) and plasmid profiles of S. Enteritidis strains isolated from patients, food, and the environment in Siberia and the Far East of Russia obtained during Salmonella monitoring between 1990 and 2017. A total of 345 S. Enteritidis isolates were tested by the disk diffusion method with a set of 15 antibiotics using EUCAST breakpoints v. 10 and by plasmid profile analysis using the alkaline lysis method. The results have shown a substantial decrease in susceptibility to aminoglycosides and quinolones during the study period. No significant differences were found in the susceptibility of strains between regions as well as in the its correlation with different plasmid types of the pathogen. Several S. Enteritidis strains were found to be resistant to ampicillin, kanamycin, tetracycline, chloramphenicol, and cephalosporins. All tested S. Enteritidis strains were susceptible only to imipenem. In this study, we observed a relatively low level of AMR in S. Enteritidis strains isolated in Siberia and the Far East of Russia. Nevertheless, it is important to continue the molecular genetic monitoring and AMR surveillance of S. Enteritidis to track further increases in AMR using conventional phenotypic susceptibility testing and by introducing whole-genome sequencing to identify AMR mechanisms.

Application of Whole-Genome Sequencing in the National Molecular Tracing Network for Foodborne Disease Surveillance in China

National Molecular Tracing Network for Foodborne Disease Surveillance (TraNet) was launched in 2013, which is the only real-time whole-genome sequencing (WGS)-based subtyping network in China for effective foodborne disease surveillance. TraNet covers three levels of public health laboratories, national, provincial, and municipal. The TraNet national databases have a total of more than 54,000 entries representing seven common foodborne bacteria from humans, food, and environments. Raw sequence data are uploaded to TraNet by Data Delivery Center. Assembled sequence data, pulsed-field gel electrophoresis (PFGE) profiles, antibiotic resistance patterns, and epidemiological data are submitted to national pathogen-specific databases managed by China National Center for Food Safety Risk Assessment. PFGE patterns and WGS-based subtyping are compared for rapid differentiation of clusters of geographically diverse foodborne infections. WGS-based TraNet has played significant roles in improving foodborne disease surveillance in China for rapid outbreak investigation, source tracking, and cluster analysis of particular pathogens across the country.

Antibiotic Susceptibility Profile and Tetracycline Resistance Genes Detection in Salmonella spp. Strains Isolated from Animals and Food

Salmonella spp. is among the leading causes of foodborne infections in humans and a large number of animals. Salmonella spp. is a pathogen involved in the dissemination of antimicrobial resistance because it can accumulate antibiotic resistance genes (ARGs). In this study, the antibiotic resistance profile to 15 antibiotics, belonging to six different classes, of 60 strains of Salmonella spp. collected from pets, farm animals, wildlife, and food in Sicily (Italy) was investigated by the Kirby-Bauer method. Given that almost 33.3% of the Salmonella spp. strains were resistant to tetracycline, Real-Time PCR analysis was applied on all the 60 strains to detect the presence of eight selected tet resistance genes. Besides, the presence of the int1 gene, related to the horizontal gene transfer among bacteria, was also investigated in all the strains by Real-Time PCR analysis. Our data showed that 56% of the isolated strains harbored one or more tet resistance genes and that these strains were most frequently isolated from animals living in close contact with humans. Concerning int1, 17 strains (28.3%) harbored this genetic element and eight of these simultaneously contained tet genes. The results of this study highlight the importance of using a molecular approach to detect resistance genetic determinants, whose spread can increase the diffusion of multidrug-resistant strains. Besides, the study of zoonotic bacteria such as Salmonella spp. which significantly contribute to ARGs dissemination should always follow a One Health approach that considers the health of humans, animals, and the environment to be closely related.