Outbreaks of antimicrobial resistant Salmonella Choleraesuis in wild boars piglets from central-western Spain

Antimicrobial resistance in wild game mammals: a glimpse into the contamination of wild habitats in a systematic review and meta-analysis

BACKGROUND

Wild game meat has over the years gained popularity across the globe as it is considered a food source with high protein content, low fat content, and a balanced composition of fatty acids and minerals, which are requirements for a healthy diet. Despite this popularity, there is a concern over its safety as many species of wildlife are reservoirs of zoonotic diseases including those of bacterial origin, more so antibiotic-resistant bacteria.

METHODS

This study aimed to describe the prevalence of antibiotic-resistant bacteria in mammalian wild game, following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

The overall pooled prevalence of antibiotic resistance was established at 59.8% while the prevalence of multidrug resistance (MDR) was 17.2%. Resistance was reported in 32 wild game species and the meta-analysis revealed the highest prevalence of antibiotic resistance in Yersinia spp. (95.5%; CI: 76.8 - 100%) followed by Enterococcus spp. (71%; CI: 44.1 - 92%), Salmonella spp. (69.9%; CI: 44.3 - 90.0%), Staphylococcus spp. (69.3%; CI: 40.3 - 92.3%), and Escherichia coli (39.5%; CI: 23.9 - 56.4%). Most notably, resistance to highest priority, critically important antimicrobials, was recorded in all genera of bacteria studied. Additionally, a significantly higher prevalence of antibiotic resistance was observed in studies conducted in remote settings than those in the vicinity of anthropogenic activities, pointing to extensive contamination of wild habitats.

CONCLUSION

This review shows the presence of antibiotic resistance and the carriage of antimicrobial resistance (AMR) genes by bacteria isolated from mammalian wild game species. This is a cause for concern if critical steps to prevent transmission to humans from meat and meat products are not applied in the wild game meat production chain. The extensive occurrence of antibiotic resistance in the wild calls for expansion and adaptation of future AMR surveillance plans to include areas with various anthropogenic pressures including in sylvatic habitats.

Systematic Review of the Occurrence and Antimicrobial Resistance Profile of Foodborne Pathogens from Enterobacteriaceae in Wild Ungulates Within the European Countries

Game meat is derived from non-domesticated, free-ranging wild animals and plays an important role in human nutrition, but it is recognized as a source of food-borne and drug-resistant pathogens impacting food safety. The present review aimed to provide a comprehensive analysis of the frequency of isolation and antimicrobial resistance (AMR) profiles of major foodborne pathogens from the Enterobacteriaceae, including Salmonella, Escherichia, and Yersinia genera, in wild ungulates, across Europe in the 21st century. A systematic search was conducted via the Google Scholar database using the PRISMA guidelines. In this regard, the content of a total of 52 relevant scientific publications from both European Union (n = 10) and non-European Union countries (n = 3) was processed, highlighting the main scientific achievements and indicating knowledge gaps and future perspectives. The studies highlighted that Salmonella spp. was the most commonly encountered pathogen, and significant AMR levels were noticed for the isolated strains, especially against penicillin (32.8%) and amoxicillin (32.1%). This review underscores the importance of monitoring the presence of food-borne pathogens and their AMR in wildlife as important public health and food safety concerns.

Generation and evaluation of Salmonella entericaserovar Choleraesuis mutant strains as a potential live-attenuated vaccine

BACKGROUND

Salmonella entericaserovar Choleraesuis (S.C) is a swine enteric pathogen causing paratyphoid fever, enterocolitis, and septicemia in piglets. S. C is mainly transmitted through the fecal-oral route. Vaccination is an effective strategy for preventing and controlling Salmonella infection.

RESULTS

Herein, we used CRISPR-Cas9 technology to knockout the virulence regulatory genes, rpoS, and slyA of S. C and constructed the ∆rpoS, ∆slyA, and ∆rpoS ∆slyA strains. The phenotypic characteristics of the mutant strains remained unchanged compared with the parental wild-type strain. In vivo study, unlike the wild-type strain, the ∆slyA and ∆rpoS ∆slyA strains alleviated splenomegaly, colon atrophy, and lower bacterial loads in the spleen, liver, ileum, and colon. These mutant strains survived in Peyer's patches (PPs) and mesenteric lymph nodes (MLN) for up to 15 days post-infection. Furthermore, the immunization of the ∆rpoS ∆slyA strain induced robust humoral and cellular immune responses.

CONCLUSIONS

Consequently, vaccination with ∆rpoS ∆slyA conferred a high percentage of protection against lethal invasive Salmonella, specifically S. C, in mice. This study provided novel insights into the development of live-attenuated vaccines against the infection of S. C.

Antimicrobial resistance profile in Salmonella enterica serovar Choleraesuis isolates from diseased pigs in Taiwan

This study investigated antimicrobial resistance in Salmonella enterica serovar Choleraesuis (S. Choleraesuis) isolates from diseased pigs in Taiwan (2015-2020). Among 272 isolates, florfenicol (96.7%), enrofloxacin (96.3%), doxycycline (91.2%), gentamicin (84.6%), and tiamulin (80.5%) exhibited high resistance. 99.3% of the isolates were resistant to at least one antibiotic, and 97.8% of the isolates were multidrug resistant. This study illustrated that S. Choleraesuis isolates exhibited high resistance to antimicrobials currently used in the Taiwanese swine industry.

Phenotypic and genetic characterization of antimicrobial resistance in Salmonella enterica serovar Choleraesuis isolates from humans and animals in Spain from 2006 to 2021

OBJECTIVES

While an increase in the levels of MDR in Salmonella enterica sevorar Choleraesuis has been reported in Europe, little is known about the situation in Spain. Therefore, we first aimed to assess the phenotypic resistance profile and to determine the presence of genetic determinants of resistance of S. Choleraesuis isolates collected in animal and human. Our second objective was to identify and characterize clusters of highly related isolates.

METHODS

We analysed 50 human and 45 animal isolates retrieved from 2006 to 2021 using the disc diffusion method and performed WGS followed by analyses of genetic determinants and phylogenetic analysis.

RESULTS

All isolates were of ST145 and corresponded to the variant Kunzendorf. Swine isolates harboured a significantly higher number of antimicrobial resistance genes than human isolates, and often carried plasmid replicons of the IncHI2/IncHI2A type (42% of all animal isolates). In addition, we identified several MDR S. Choleraesuis strains circulating in humans and swine between 2006 and 2021. The phylogenetic analyses identified four clades associated with specific patterns of resistance genes and plasmid replicons. The clades also included isolates that differed in terms of year and region of isolation as well as host of origin.

CONCLUSIONS

This One Health approach highlights that reducing human MDR S. Choleraesuis infections may require the adoption of strategies that not only seek to prevent cases in humans but also to characterize and reduce the infection burden in swine.

Salmonella enterica subspecies enterica serovar Choleraesuis in a Swedish gilt-producing herd, a case report

BACKGROUND

When Salmonella enterica subspecies enterica serovar Choleraesuis (S. Choleraesuis) was detected in faecal samples collected within the Swedish Salmonella surveillance program from a gilt multiplying herd in September 2020, S. Choleraesuis had not been detected in domestic pigs or wild boar in Sweden for over 40 years. This report describes the subsequent investigation, identification of possible entry routes and measures undertaken to eliminate the pathogen from the herd.

CASE PRESENTATION

In accordance with Swedish regulations, pig movements to and from the farm were restricted, internal biosecurity measures were enhanced, and a test-and-remove strategy was implemented. Testing included repeated faecal sampling, tissue samplings from all dead or euthanized pigs, and serological sampling of replacement gilts. Epidemiological investigations included scrutinising of production records, employee interviews, analysing feed and environmental samples, faecal samples from the herd's purebred gilt supplier, and tissue and faecal samples from wild boars in the adjacent area. Testing of in-contact herds receiving gilts (n = 15) or 30-kg pigs (n = 7) from the multiplier included whole-herd faecal sampling and tissue cultures from pigs that died with signs of septicaemia. In total, S. Choleraesuis was detected in 12/4200 faecal and 5/1350 tissue samples from the herd, and the corresponding groups of pigs were euthanized. All feed and environmental samples as well as samples from the gilt supplier were negative. Testing of contact herds resulted in the identification and culling of one group of S. Choleraesuis-positive gilts. Replacement gilts introduced to the herd from January until May 2021 remained serologically negative during a surveillance-period of five months.

CONCLUSION

Although speculative, the epidemiological investigation identified indirect transmission from wild boar as possible source of introduction to the herd. Whole-genome sequencing of S. Choleraesuis isolates from wild boar in the area showed that they clustered with isolates from the herd. Repeated testing of the herd indicated that the test-and-remove strategy was successful. In August 2021, all restrictions were removed, and the herd was re-instated as a gilt producing herd. Compensation from the Swedish state to the farmer for production losses, culled animals and extra costs associated with the elimination cost totalled SEK 7 992 234.

Exogenous D-ribose promotes gentamicin treatment of several drug-resistant Salmonella

The metabolic microenvironment of bacteria impacts drug efficacy. However, the metabolic mechanisms of drug-resistant Salmonella spp. remain largely unknown. This study characterized the metabolic mechanism of gentamicin-resistant Salmonella Choleraesuis and found that D-ribose increased the gentamicin-mediated killing of this bacteria. Non-targeted metabolomics of homologous gentamicin-susceptible Salmonella Choleraesuis (SCH-S) and gentamicin-resistant S. Choleraesuis (SCH-R) was performed using UHPLC-Q-TOF MS. The metabolic signature of SCH-R included disrupted central carbon metabolism and energy metabolism, along with dysregulated amino acid and nucleotide metabolism, vitamin and cofactor metabolism, and fatty acid synthesis. D-ribose, the most suppressed metabolite in SCH-R, was shown to strengthen gentamicin efficacy against SCH-R and a clinically isolated multidrug-resistant strain. This metabolite had a similar impact on Salmonella. Derby and Salmonella. Typhimurium. D-ribose activates central carbon metabolism including glycolysis, the pentose phosphate pathway (PPP), and the tricarboxylic acid cycle (TCA cycle), increases the abundance of NADH, polarizes the electron transport chain (ETC), and elevates the proton motive force (PMF) of cells, and induces drug uptake and cell death. These findings suggest that central carbon metabolism plays a critical role in the acquisition of gentamicin resistance by Salmonella, and that D-ribose may serve as an antibiotic adjuvant for gentamicin treatment of resistant bacterial infections.

Evaluation of the Occurrence of Staphylococcaceae with Reduced Susceptibility to Cefoxitin in Wild Ungulates in Brandenburg, Germany, Based on Land Use-Related Factors

Interactions between natural and human-used environments have a significant influence on the spread of antimicrobial resistance in wild ecosystems. Despite current knowledge, fundamental questions about the degree of impact of land use-related factors on the spread of antimicrobial-resistant staphylococci in European wild game animal populations have not yet been answered with certainty. In this study, we evaluated the occurrence of Staphylococcaceae showing reduced susceptibility to cefoxitin in nasal swabs of fallow deer (Dama dama), red deer (Cervus elaphus), roe deer (Capreolus capreolus), and wild boar (Sus scrofa) hunted in Brandenburg, Germany. Evaluations were focused on the use of open-source data regarding the extent as well as the degree of land use, especially for settlement or animal husbandry. Results showed that the detection rate of Staphylococcaceae showing a non-wild-type phenotype for cefoxitin differed between animal species of the studied hunting districts. Statistical analyses of results combined with data on land use features revealed that a high density of cattle or poultry in a county may be associated with an increased detection rate in roe deer or wild boar, respectively. Furthermore, positive correlations were determined between the prevalence of non-wild-type Staphylococcaceae in roe deer or fallow deer and the proportional extent of surface water bodies in the corresponding area. The presented approach establishes a general basis for a risk-oriented assessment of the effects of human activities on the epidemiology of transmissible microorganisms in the human-animal-environment interface, including antimicrobial-resistant bacteria. IMPORTANCE Intensive research regarding the impact of land use-related factors on the prevalence and distribution of antimicrobial-resistant Staphylococcaceae in game ungulate populations is necessary for adequately determining risks related to interactions between wild animals, domestic animals, and humans in common geographic locations. This systematic approach for the analysis of the observations in specific hunting districts of Brandenburg, Germany, adds an innovative value to the research strategy of antimicrobial resistance in wild game animals, which is in accordance with current recommendations worldwide. Thus, results and information obtained in this study build a relevant foundation for future risk assessment regarding the safety of game products. Furthermore, the data generated represent an important basis for improving existing guidelines in land use practices and hunting practices. The use of existing open source data collections provided by official governmental and nongovernmental entities increases not only the impact but also the applicability and comparability of information beyond the regional level.

Dissemination of antimicrobial-resistant isolates of Salmonella spp. in wild boars and its relationship with management practices

Antimicrobial resistance (AMR) is a global concern and controlling its spread is critical for the effectiveness of antibiotics. Members of the genus Salmonella are broadly distributed, and wild boar may play an important role in its circulation between peri-urban areas and the environment, due to its frequent interactions both with livestock or human garbage. As the population of these animals is rising due to management on certain hunting estates or the absence of natural predators, the aim of the present work is to identify the mechanisms of AMR present and/or expressed in Salmonella spp. from wild boar populations and to determine the possible role of management-related factors applied to different game estates located in central Spain. The detection of Salmonella spp. was carried out in 121 dead wild boar from 24 game estates, and antimicrobial resistance traits were determined by antibiotic susceptibility testing and screening for their genetic determinants. The effects of feeding supplementation, the proximity of livestock, the existence of a surrounding fence and the density of wild boar on the AMR of the isolates were evaluated. The predominant subspecies and serovar found were S. enterica subsp. enterica (n = 69) and S. choleraesuis (n = 33), respectively. The other subspecies found were S. enterica subsp. diarizonae, S. enterica subsp. salamae and S. enterica subsp. houtenae. AMR was common among isolates (75.2%) and 15.7% showed multi drug resistance (MDR). Resistance to sulphonamides was the most frequent (85.7%), as well as sul1 which was the AMR determinant most commonly found. Plasmids appeared in 38.8% of the isolates, with IncHI1 being the replicon detected with the highest prevalence. The AMR of the isolates increased when the animals were raised with feeding supplementation and enclosed by fences around the estates.

First Detection of Salmonella enterica Serovar Choleraesuis in Free Ranging European Wild Boar in Sweden

Following the first detection of Salmonella enterica subsp. enterica, serovar Choleraesuis (S. Choleraesuis) in a Swedish pig herd for more than 40 years and subsequent detection of the same serotype in an enclosure with kept wild boar, a national surveillance for S. Choleraesuis in free living wild boar was launched. A total of 633 wild boar sampled within the active and the enhanced passive surveillance were examined for Salmonella enterica serovars by culture. Of these, 80 animals were culture positive for S. Choleraesuis var. Kunzendorf. All positive animals, including those in the original outbreaks, originated from counties located in the southern and eastern parts of Sweden. Fifty-eight isolates were selected for sequence typing, revealing a relatively homogenous population of S. Choleraesuis with two distinct genetic clusters containing isolates from the southern counties in one and the counties further northeast in the other. Sequenced isolates from domestic pig farms all clustered with wild boar in the same region. S. Choleraesuis appears highly contagious in dense wild boar populations, making it a relevant model for other infectious diseases that may be transmitted to pigs. The many potential routes of introduction and spread of S. Choleraesuis warrant further investigations in order to prepare for other disease threats.

Nonspecific protection of heat-inactivated Mycobacterium bovis against Salmonella Choleraesuis infection in pigs

Trained immunity is the capacity of innate immune cells to produce an improved response against a secondary infection after a previous unrelated infection. Salmonellosis represents a public health issue and affects the pig farming industry. In general, vaccination against salmonellosis is still facing problems regarding the control of distinct serovars. Therefore, we hypothesized that an immunostimulant based on heat inactivated Mycobacterium bovis (HIMB) could have an immune training effect in pigs challenged with Salmonella enterica serovar Choleraesuis (S. Choleraesuis) and decided to explore the amplitude of this non-specific immune response. For this purpose, twenty-four 10 days-old female piglets were randomly separated in three groups: immunized group (n = 10) received orally two doses of HIMB prior to the intratracheal S. Choleraesuis-challenge, positive control group (n = 9) that was only challenged with S. Choleraesuis, and negative control group (n = 5) that was neither immunized nor infected. All individuals were necropsied 21 days post-challenge. HIMB improved weight gain and reduced respiratory symptoms and pulmonary lesions caused by S. Choleraesuis in pigs. Pigs immunized with HIMB showed higher cytokine production, especially of serum TNFα and lung CCL28, an important mediator of mucosal trained immunity. Moreover, immunized pigs showed lower levels of the biomarker of lipid oxidation malondialdehyde and higher activity of the antioxidant enzyme superoxide dismutase than untreated challenged pigs. However, the excretion and tissue colonization of S. Choleraesuis remained unaffected. This proof-of-concept study suggests beneficial clinical, pathological, and heterologous immunological effects against bacterial pathogens within the concept of trained immunity, opening avenues for further research.

Genomic insights into Salmonella Choleraesuis var. Kunzendorf outbreak reveal possible interspecies transmission

Salmonella enterica serovar Choleraesuis is a host-adapted serovar that causes serious infections in domestic pigs and wild boars. Here, we investigated an outbreak of salmonellosis in domestic pigs in Slovenia, 2018-2019. To assess the outbreak, 18 isolates from domestic pigs, wild boars, wild boar meat and a human patient underwent whole-genome sequencing (WGS). All isolates were of sequence type (ST) 145 and harbored no antimicrobial resistance genes or AMR-associated mutations. A single transmission cluster (≤ 6 alleles) of spatially (< 100 km) and temporally linked isolates was observed, comprising isolates of pig (n = 9), wild boar (n = 2) and human (n = 1) origin, and suggesting possible interspecies transmission. In all outbreak-related animal cases, septicemic salmonellosis was observed, accompanied in some cases by enteric symptoms. All pig isolates were linked to a single intensive breeding farm that distributed growers to small family farms. The same transport vehicles were used to distribute growers to family farms and also to transport livestock between neighboring countries. Both isolates that originated from the imported wild boar meat were genetically distant (≥ 122 alleles) from the outbreak cluster. The present results indicate the importance of screening domestic pigs and proper disinfection of transport vehicles to control the spread of S. Choleraesuis.

What WGS Reveals about Salmonella enterica subsp. enterica in Wildlife in Germany

The aim of this study was to gain an overview of the genetic diversity of Salmonella found in wildlife in Germany. We were particularly interested in exploring whether wildlife acts as a reservoir of certain serovars/subtypes or antimicrobial resistance (AMR) genes. Moreover, we wanted to explore the potential of Salmonella in spreading from wildlife to livestock and humans. To answer these questions, we sequenced 260 Salmonella enterica subsp. enterica isolates sampled between 2002 and 2020 from wildlife across Germany, using short-read whole genome sequencing. We found, consistent with previous findings, that some Salmonella sequence types are associated with certain animal species, such as S. Choleraesuis ST145 with wild boar and S. Enteritidis ST183 with hedgehogs. Antibiotic resistance was detected in 14.2% of all isolates, with resistance against important WATCH group antibiotics present in a small number of isolates. We further found that wildlife isolates do not form separate phylogenetic clusters distant to isolates from domestic animals and foodstuff, thus indicating frequent transmission events between these reservoirs. Overall, our study shows that Salmonella in German wildlife are diverse, with a low AMR burden and close links to Salmonella populations of farm and food-production environments.

A Salmonella enterica subspecies enterica serovar Choleraesuis outbreak in weaned piglets in Serbia: clinical signs, pathologic changes, and microbiologic features

Salmonella enterica subspecies enterica serovar Choleraesuis is rarely detected in Europe, but the clinical disease has been reported in wild boars. We describe here the clinical findings, pathologic changes, and microbiologic features of swine salmonellosis caused by S. enterica serovar Choleraesuis in weaned piglets in Serbia. In April 2019, on a large farrow-to-finish pig farm, increased mortality was reported in weaned piglets, marked by lethargy, anorexia, pyrexia, and respiratory distress. Gross pathology revealed dermal cyanosis, mesenteric lymphadenopathy, splenomegaly, hepatomegaly, interstitial pneumonia, and colitis. By direct culturing of lung, liver, spleen, and lymph nodes, S. enterica ser. Choleraesuis variant Kunzendorf was isolated after years of absence of the disease in pig farms in Europe. The source of this salmonellosis outbreak caused by S. enterica ser. Choleraesuis remains unknown.

Prevalence and Antimicrobial Resistances of Salmonella spp. Isolated from Wild Boars in Liguria Region, Italy

Salmonella spp. is an important zoonotic agent. Wild boars might host this pathogen in the intestinal tract and might represent a risk for Salmonella spp. transmission to humans. Wild boars are widely spread in Liguria, due to the environmental characteristics of the region. The aim of the study was the isolation, typing, and investigation of antimicrobial susceptibility of the isolated strains of Salmonella spp. During the 2013–2017 hunting seasons, 4335 livers of wild boars were collected and analyzed for the presence of Salmonella spp. A total of 260 strains of Salmonella spp. were isolated and characterized, with a prevalence of 6%. The isolated strains belonged to all six Salmonella enterica subspecies. Most of them were identified as Salmonella enterica subs. enterica of which 31 different serotypes were identified. The dominating serotype identified was S. Enteritidis. The antimicrobial resistance profiles of the isolated strains were analyzed against sixteen molecules. Of the isolated strains, 94.6% were resistant to at least one of the tested antimicrobials. This study showed the circulation of resistant Salmonella spp. strains in the wild boar population living in this area of Italy, underling the potential risk for these animals to disseminate this pathogen and its antimicrobial resistances.

Re-Emergence of Salmonellosis in Hog Farms: Outbreak and Bacteriological Characterization

Clinical salmonellosis has been increasing significantly in Brazil in recent years. A total of 130 outbreaks distributed among 10 swine-producing states were investigated. One representative Salmonella isolate from each outbreak was characterized through serotyping, antimicrobial resistance profiles, PFGE, and WGS. From 130 outbreaks: 50 were enteric, 48 were septicemic, 17 cases were characterized as hepato-biliary invasive, 13 as nodal and two were not classified. The most prevalent serovars were a monophasic variant of S. typhimurium (55/130), Choleraesuis (46/130), and Typhimurium (14/130). Most of the strains (86.92%) demonstrated a high rate of multi-drug resistance. The identification of a major Choleraesuis clonal group in several Brazilian states sharing the same resistance genes suggested that these strains were closely related. Six strains from this clonal group were sequenced, revealing the same ST-145 and 11 to 47 different SNPs. The detected plasmid type showed multiple marker genes as RepA_1_pKPC-CAV1321, the first to be reported in Salmonella. All AMR genes detected in the genomes were likely present on plasmids, and their phenotype was related to genotypic resistance genes. These findings reveal that salmonellosis is endemic in the most important pig-producing states in Brazil, emphasizing the need to make data available to aid in reducing its occurrence.

Spread of Antimicrobial Resistance by Salmonella enterica Serovar Choleraesuis between Close Domestic and Wild Environments

The Salmonellaenterica serovar Choleraesuis affects domestic pig and wild boar (WB), causing clinical salmonellosis. Iberian swine production is based on a free-range production system where WB and Iberian pig (IP) share ecosystems. This study focuses on the negative impact on the pork industry of infections due to this serotype, its role in the spread of antibiotic resistance, and its zoonotic potential. Antibiotic resistance (AR) and genetic relationships were analyzed among 20 strains of S. Choleraesuis isolated from diseased WB and IP sampled in the southwest region of the Iberian Peninsula. AR was studied using the Kirby-Bauer method with the exception of colistin resistance, which was measured using the broth microdilution reference method. Resistance and Class 1 integrase genes were measured using PCR, and the genetic relationship between isolates and plasmid content by pulsed field gel electrophoresis. The results show a higher incidence of AR in isolates from IP. Phylogenetic analysis revealed seven profiles with two groups containing isolates from IP and WB, which indicates circulation of the same clone between species. Most pulsotypes presented with one plasmid of the same size, indicating vertical transmission. AR determinants bla_TEM and tetA were routinely found in IP and WB, respectively. One isolate from IP expressed colistin resistance and presented the mcr-1 gene carried by a plasmid. This study suggests that S. Choleraesuis circulates between WB and IP living in proximity, and also that the mobilization of AR genes by plasmids is low. Furthermore, the detection of plasmid-mediated colistin resistance in bacteria from IP is alarming and should be monitored.

Salmonella seroprevalence in wild boar from Southeast Spain depends on host population density

Salmonellosis is the second most prevalent zoonosis in Europe and it has considerable economic and health implications for its monitoring and control as well as being among the most prevalent pathogens on livestock farms. The wild boar (Sus scrofa) has been identified as a competent host and spreader of Salmonella spp. There has been a significant increase in wild boar population in Europe in recent decades, and it is even present in urban areas. This study evaluates the spatial distribution of the seroprevalence of Salmonella spp. in wild boar from Murcia (Southeast Spain) and its relationship with host-related risk factors (sex, age, location and density). The presence of antibodies against S. Typhimurium and Choleraesuis in 269 serum of wild boars hunted in Murcia between 2015 and 2019 were analyzed using a commercial ELISA test (PrioCHECK porcine Salmonella kit). The seroprevalence were spatially distributed using Kernel function, and wild boar density using Gaussian kernel estimates (spatialEco version 1.1.1). The risk function was estimated as the ratio between the intensity of positive samples and the wild boar density The overall seroprevalence was 19.3% (IC95% 16.9-21.8), showing a significant spatial aggregation. The highest seroprevalence detected was 51.8% (IC95% 42.2-61.5) in a specific area with high risk of infection (76-100%) and was related to the wild boar density. Only marginal differences were detected for sex and age. The use of ELISA combined with QGIS (version 3.6.0) has allowed the identification of areas of Salmonella occurrence associated with high density as risk factor.

Simple differentiation of Salmonella Typhi, Paratyphi and Choleraesuis from Salmonella species using the eazyplex TyphiTyper LAMP assay

Introduction. Identification of typhoidal Salmonella (TS) serovars and their discrimination from non-typhoidal Salmonella (NTS) is conventionally performed by seroagglutination. This method is labour-intensive, requires technical experience and can be inconclusive in some cases. Molecular assays may be reliable alternative diagnostic tools.

Aim. This study was designed to evaluate the eazyplex TyphiTyper based on loop-mediated isothermal amplification (LAMP) for fast identification of TS and S. Choleraesuis in culture.

Methodology. A total of 121 Salmonella strains and 33 isolates of other Enterobacterales species were tested by the eazyplex TyphiTyper. Simulated and clinical blood cultures (BCs) were used to examine the performance of the assay for diagnosis of systemic infection. Sample preparation took about 5 min and the test running time was 20 min. Amplification was measured by real-time fluorescence detection.

Results. All TS and S. Choleraesuis strains were correctly identified. The most common NTS S. Typhimurium (n=34) and S. Enteritidis (n=15) were detected as Salmonella species without any false positive result for TS targets. Cross-reactions of NTS with TS were only rarely observed. Direct testing of positive BCs gave correct results. Sensitivities and specificities of the assay were as follows: 100 and 99.3 % for S. Typhi, 100 and 98.7 % for S. Paratyphi A, 100 and 97.3 % for S. Paratyphi B, 100 and 100 % for S. Paratyphi C, 100 and 100 % for S. Choleraesuis, and 100 and 100 % for Salmonella species, respectively.

Conclusion. The eazyplex TyphiTyper is very easy to perform and allows the rapid identification of TS and S. Choleraesuis isolates.

Wild boar as a reservoir of antimicrobial resistance

Antimicrobial resistance (AMR) has been recognized as an emerging and growing problem worldwide. Knowledge concerning AMR bacteria circulating in wildlife is currently limited, although it could provide important insights into AMR emergence and persistence. Across Europe, wild boar (Sus scrofa) populations have dramatically increased their distribution and number over the last decades. In the context of AMR dynamics, wild boar is a perfect model species to unveil the emergence, spread and persistence of AMR at the human-livestock-wildlife interface. Here, we summarize the current knowledge on the importance of wild boar as a reservoir of antimicrobial resistant bacteria, and its possible use as sentinel species for surveillance. Analyses of available data showed a rising interest on this topic in the last years, highlighting the growing concern on wild boar potential role as AMR facilitator and it is foreseen that the importance of antimicrobial resistance research in wild boar will continue to increase in years to come. Available studieshave been focused on specific bacterial species, particularlyE. coli, Salmonellaspp. andEnterococcusspp., bioindicators of AMR, and have been mainly conducted in three countries: Spain, Portugal and Germany.Strikingly, AMR surveillance in wild boar is uneven and still poorly allocated as many wild boar high-density countries do not yet have publications on the topic.Overall, accumulated data showed thatwild boar are carriers of antimicrobial resistant bacteria, withvariation in the prevalence of bacterial species and thepercentage of resistance to different antibiotics. Thelack of harmonized sampling and testing protocols makes it difficult to compare AMR in wild boar.The need for the establishment of standardised protocols keen to provide quantitative comparable data is highlighted. We finally suggest the long-term monitoring of wild boar as a sentinel species for AMR surveillance in order to inform public policies on this topic.

Insight into an outbreak of Salmonella Choleraesuis var. Kunzendorf in wild boars

An unusual mortality of wild boars occurred in Italy from 2012 to 2015 due to Salmonella Choleraesuis infection. In order to confirm the occurrence of an outbreak of S. Choleraesuis in wild boars and to epidemically characterise the unique S. Choleraesuis biovar, a collection of isolates belonging to wild boars was investigated from the phenotypic, molecular and genomic points of view (PFGE and WGS). Moreover, the possibility of transmission to domestic pigs and humans, temporally and geographically close to the wild boar epidemic, was tested by also including in the panel isolates from infected domestic pigs and from one human case of infection. Wild boar isolates displayed a high genetic correlation, thus suggesting they are part of the same outbreak, with a common invasiveness potential. Conversely, no correlation between pig isolates and those from the other sources (wild boars and human) was found. However, the phylogenetic and PFGE analyses suggest a high degree of similarity between the human and the investigated wild boar outbreak isolates, implying the potential for the spread of Salmonella Choleraesuis among these species.

Exploring the importance of mixed autogenous vaccines as a potential determinant of lung consolidation in lambs using Bayesian networks

Bayesian networks are used to evaluate the effectiveness of mixed autogenous vaccines in fattening lambs to prevent the ovine respiratory syndrome. An experiment was performed with 460 fattening lambs, which were clustered into four groups according to the kind of vaccine received (Pasteurella spp., Mycoplasma spp., Mixed Mycoplasma-Pasteurella or placebo). After slaughtering, lungs were collected, and macroscopic and microscopic studies were performed. A microbiological study was carried out to evaluate the presence of Mycoplasma spp. and Pasteurellaceae by conventional culture and identification by nested polymerase chain reaction. To the best of the authors' knowledge, Bayesian networks have not been used to evaluate the effect of vaccines on the absence/presence of lung consolidation. Our results revealed that the use of mixed autogenous vaccines can decrease lung consolidation from 15.75% (12.42-19.08) to 9.24% (6.59-11.89). Therefore, the use of these autogenous vaccines in farms could be considered an effective control tool against ovine respiratory syndrome.

Prevalence of Salmonella spp. in tonsils, mandibular lymph nodes and faeces of wild boar from Spain and genetic relationship between isolates

The importance of wild boars as game species in Spain is well known. Their feeding habits and intrusive behaviour, together with a progressively wider spreading of populations, increases the interactions of these animals with livestock and humans. Considering that wild boars could have a potential role in the transmission of certain pathogens as salmonellae, the aims of this study were to determine the prevalence of Salmonella spp. in wild boars hunted in central-western Spain, the occurrence of this pathogen in tonsils, mandibular lymph nodes and faeces (as markers for transmission risk), and to define the phylogenetic relationships among isolated strains, in order to investigate the circulation pathways of bacteria among tissues, animals and estates. Samples from 1,041 hunted wild boars were analysed for the presence of Salmonella spp. by bacteriological culture. Isolates were confirmed by PCR and serotyped in the Spanish national reference laboratory. The genetic relationships between strains were determined by PFGE. The results showed a 7.7% of positive animals (81 wild boars), being tonsils the organ most frequently colonised by Salmonella spp. (18.7%), followed by lymph nodes (5.1%) and faecal samples (2.9%). Serovars Enteritidis and Newport were the most frequent amongst the 34 different serovars obtained. The pulsed-field gel electrophoresis (PGFE) analysis showed a great genetic diversity, with serovars that exhibited different pulsotypes when isolated from different estates and multiple serovars in the same estate. In conclusion, this study reveals the importance of wild boars as carriers and possible transmitters of virulent and/or antimicrobial-resistant clones of Salmonella spp. to livestock and humans.

Outbreaks of antimicrobial resistant Salmonella Choleraesuis in wild boars piglets from central-western Spain

Salmonella enterica serovar Choleraesuis is the aetiological agent of swine paratyphoid being a highly invasive zoonotic pathogen. Wild boar natural populations are experiencing a demographical expansion as well as some farms are breeding this species to release for hunting with management sometimes identical to that of domestic pigs, including supplementation, grouping, and antibiotic treatments. This situation increases the chance of contact between wild boars and livestock, and potentially induces stress, with different sanitary consequences. The present work aims to describe the clinical features of recent outbreaks caused by S. Choleraesuis in wild boar from central-western Spain, as well as the antimicrobial resistance and phylogenetic relationships of isolates involved. 28 strains of S. Choleraesuis were isolated from 28 different wild boars belonging to 10 different game states located in central western Spain and submitted to the Clinical Veterinary Hospital (CVH) of the University of Extremadura. Samples were taken from different organs and cultured according to the ISO 6579:2002 procedure. Suspicious colonies were identified by PCR and antimicrobial resistance was evaluated by disc diffusion susceptibility test and the presence of the main resistance genes as well as 18 plasmid replicons frequently found among the Enterobacteriaceae was verified by PCR. Pulsed field gel electrophoresis was applied to determine the genetic relationship between isolates. The outbreaks under study were characterized by high mortality (35%-84%) and a septicaemic presentation. S. Choleraesuis was isolated from all the wild boars analysed, and 26 of the 28 isolates presented resistance to at least one antibiotic. The predominant resistances found were against sulphonamide, streptomycin, tetracycline, and doxicicline and sul1, strA-strB, and tetA were the most prevalent resistance genes among isolates. 10 strains carried FIIA, FIB+H/1 or FIIA+H/1 plasmids. PFGE classified the isolates into four different profiles, grouped into two clusters. This results show that prevention against S. Choleraesuis must be considered in the sanitary programs of the wild boar breeders.