OBJECTIVE: We aimed to characterise Yersinia enterocolitica from human clinical specimens in Switzerland using epidemiological, microbiological and whole-genome sequencing (WGS) data.
METHODS: Isolates (n = 149) were collected between January 2019 and December 2023. Epidemiological data was noted and strains were characterized by biochemical and serological typing, antimicrobial susceptibility testing (AST), and WGS-based analysis.
RESULTS: Most of the isolates (86%) were from stool specimens and 52% were from male patients. The patients\' median age was 28 years (range < 1-94 years). Typing assigned the isolates to bioserotype 4/O:3 (44%), biotype 1A (34%), bioserotype 2/O:9 (21%), and bioserotype 3/O:3 (1%). WGS identified Y. enterocolitica (n = 147), Y. alsatica (n = 1) and Y. proxima (n = 1). Seven isolates were multidrug resistant (MDR) and harboured plasmid pAB829 carrying aph(3″)-Ib, aph(6)-Id, and tet(Y) (n = 1), pAC120 carrying aph(6)-Id and tet(A) (n = 2), or a 12.6 kb Tn2670-like transposon containing catA1, aadA12, sul1, and qacEΔ1 (n = 4). Virulence factors (VFs) included ail (n = 99), invB, (n = 145), ystA (n = 99), ystB (n = 48) and pYV-associated VFs (n = 93). MLST and cgMLST analysis showed that BT 1A strains consisted of several STs and were highly diverse, whereas BT 2/O:9 strains were all ST12 and clustered closely, and BT 4/O:3 strains mostly belonged to ST18 but were more diverse. SNP analysis revealed two highly clonal BT 4/O:3 subpopulations with wide spatio-temporal distribution.
CONCLUSIONS: Y. enterocolitica BT 1A, BT 2/O:9 and BT 4/O:3 are frequently associated with human yersiniosis in Switzerland. WGS-based subtyping of Y. enterocolitica is a powerful tool to explore the genetic diversity and the pathogenic potential of human isolates.

Yersinia enterocolitica (Y. enterocolitica) is the most frequent etiological agent of yersiniosis and has been responsible for several national outbreaks in Norway and elsewhere. A standardized high-resolution method, such as core genome Multilocus Sequence Typing (cgMLST), is needed for pathogen traceability at the national and international levels. In this study, we developed and implemented a cgMLST scheme for Y. enterocolitica. We designed a cgMLST scheme in SeqSphere + using high-quality genomes from different Y. enterocolitica biotype sublineages. The scheme was validated if more than 95% of targets were found across all tested Y. enterocolitica: 563 Norwegian genomes collected between 2012 and 2022 and 327 genomes from public data sets. We applied the scheme to known outbreaks to establish a threshold for identifying major complex types (CTs) based on the number of allelic differences. The final cgMLST scheme included 2,582 genes with a median of 97.9% (interquartile range 97.6%-98.8%) targets found across all tested genomes. Analysis of outbreaks identified all outbreak strains using single linkage clustering at four allelic differences. This threshold identified 311 unique CTs in Norway, of which CT18, CT12, and CT5 were identified as the most frequently associated with outbreaks. The cgMLST scheme showed a very good performance in typing Y. enterocolitica using diverse data sources and was able to identify outbreak clusters. We recommend the implementation of this scheme nationally and internationally to facilitate Y. enterocolitica surveillance and improve outbreak response in national and cross-border outbreaks.

Postbiotics are innovative tools in animal husbandry, providing eco-friendly solutions for disease management within the industry. In this study, a new postbiotic product was evaluated for its impact on the health of rainbow trout (Oncorhynchus mykiss). In vivo studies were conducted to assess the safety of the Weissella cibaria strains used in postbiotic production. Additionally, this study evaluated the impact of diet supplementation with 0.50% postbiotics on growth performance during a 30-day feeding trial; the gut microbial communities, immunomodulation, and protection against Yersinia ruckeri infection were evaluated. The strains did not harm the animals during the 20-day observation period. Furthermore, the effect of postbiotics on growth performance was not significant (p < 0.05). The treated group showed a significant increase in acid-lactic bacteria on the 30th day of the feeding trial, with counts of 3.42 ± 0.21 log CFU/mL. Additionally, there was an up-regulation of the pro-inflammatory cytokine IL-1β in head kidney samples after 48 h of feed supplementation, whereas cytokines IL-10, IL-8, INF-γ, and TNF-α were down-regulated. The findings indicate that rainbow trout fed with postbiotics saw an improvement in their survival rate against Y. ruckeri, with a 20.66% survival improvement in the treated group. This study proves that incorporating postbiotics from two strains of W. cibaria previously isolated from rainbow trout into the diet of fish has immunomodulatory effects, enhances intestinal microbial composition, and improves fish resistance against Y. ruckeri.

The genus Yersinia includes human, animal, insect, and plant pathogens as well as many symbionts and harmless bacteria. Within this genus are Yersinia enterocolitica and the Yersinia pseudotuberculosis complex, with four human pathogenic species that are highly related at the genomic level including the causative agent of plague, Yersinia pestis. Extensive laboratory, field work, and clinical research have been conducted to understand the underlying pathogenesis and zoonotic transmission of these pathogens. There are presently more than 500 whole genome sequences from which an evolutionary footprint can be developed that details shared and unique virulence properties. Whereas the virulence of Y. pestis now seems in apparent homoeostasis within its flea transmission cycle, substantial evolutionary changes that affect transmission and disease severity continue to ndergo apparent selective pressure within the other Yersiniae that cause intestinal diseases. In this review, we will summarize the present understanding of the virulence and pathogenesis of Yersinia, highlighting shared mechanisms of virulence and the differences that determine the infection niche and disease severity.

BACKGROUND: Three Yersinia species were identified from samples of drinking water from diverse geographic regions of Ireland. Conventional commercial biochemical identification systems classified them as Yersinia enterocolitica. Since this organism is the most common cause of bacterial gastroenteritis in some countries, further investigation was warranted. The aim of the study was to provide a microbial characterisation of three Yersinia species, to determine their pathogenicity, and to review the incidence rate of Yersinia enterocolitica detection in our region.
METHODS: Organism identification was performed using conventional commercial diagnostic systems MALDI-TOF, API 20E, API 50CHE, TREK Sensititre GNID and Vitek 2 GN, and whole genome sequencing (WGS) was performed. Historical data for detections was extracted from the lab system for 2008 to 2023.
RESULTS: All three isolates gave \"good\" identifications of Yersinia enterocolitica on conventional systems. Further analysis by WGS matched two of the isolates with recently described Yersinia proxima, and the third was a member of the non-pathogenic Yersinia enterocolitica clade 1Aa.
CONCLUSIONS: Our analysis of these three isolates deemed them to be Yersinia species not known currently to be pathogenic, but determining this necessitated the use of next-generation sequencing and advanced bioinformatics. Our work highlights the importance of having this technology available to public laboratories, either locally or in a national reference laboratory. The introduction of molecular technologies for the detection of Yersinia species may increase the rate of detections. Accurate identification of significant pathogens in environmental, public health and clinical microbiology laboratories is critically important for the protection of society.

A 14-year-old female domestic short-haired cat with a diagnosed diabetes mellitus and acromegaly was presented for lethargy and dysorexia. On clinical presentation, the patient showed hyperglycemia, hyperthermia, dull mentation, and dehydration. With the suspicion of an inflammatory or infectious complication of diabetes, she was hospitalized with constant rate infusion of insulin, and empirical ampicillin sulbactam was started. Blood culture revealed positivity for Yersinia pseudotuberculosis and the septic picture was confirmed by blood analysis, with leukocytosis, neutrophilia, and an increased serum amyloid A concentration. The isolated Y. pseudotuberculosis strain showed susceptibility to every antimicrobial tested. During the second day of hospitalization, the onset of hypoglycemia and hypotension was treated with norepinephrine and glucose in fluid therapy. The cat recovered well and was discharged with insulin and amoxicillin-clavulanate. This is the first case of septicemia associated with Y. pseudotuberculosis in a cat, suspected of developing the infection after contact with natural reservoirs such as rodents or birds. This route of transmission should be highlighted especially in relation to the zoonotic potential of the bacteria.

Enteric redmouth disease (ERM) caused by the enterobacterium Yersinia ruckeri poses a significant threat to salmonid aquaculture globally. Despite decades of experimental infection studies, key knowledge gaps remain regarding the onset of disease susceptibility and mechanisms of immunity during early developmental stages, undermining disease management efforts in all susceptible life-stages. In this study, a series of immersion challenges were conducted, challenging and re-challenging rainbow trout Oncorhynchus mykiss (Walbaum) at 7, 14 and 51 d post-hatch (dph; mean weights = 0.085, 0.1 and 2.0 g respectively) to high concentrations (1.72 × 107-1.1 × 108 CFU) of Y. ruckeri at 15°C. This study indicates the hitherto unknown initial point of susceptibility to infection as the time of first ingestion of exogenous food (14 dph), and shows that individuals surviving primary challenge at 14 dph are significantly more likely to survive re-challenge at 51 dph compared with naive individuals (hazard ratio = 1.446, p = 0.032). Other key findings include large variation in mortality between different development-stages, from 21.1% at 14 dph to 81.2% at 51 dph, and novel age-dependent symptoms not reported previously. Results from this study enhance our understanding of ERM in juvenile rainbow trout and inform the development of improved aquatic animal health management strategies, thereby contributing to the productivity and sustainability of salmonid aquaculture into the future.

OBJECTIVE: The aim of the study was to assess the epidemiological situation of yersiniosis in Poland in 2018-2020 and compare it to previous years.
METHODS: To assess the epidemiological situation of yersiniosis in Poland, data from individual case reports prepared by Sanitary Epidemiological Stations as part of routine epidemiological surveillance were used. Incidence, number of cases and data on hospitalizations by voivodship included in the bulletins \"Infectious Diseases and Poisons in Poland\" for 2015-2020 were also used.
RESULTS: In 2018-2020, a total number of 542 cases of yersiniosis were registered, including 456 intestinal and 86 extraintestinal forms. The incidence in 2018 was 0.53/100,000 in 2019 0.59/100,000 and in 2020 0.29/100,000. The number of cases in 2020 compared to 2019 decreased by 52%, and compared to 2018 by 45.8%. The percentage of hospitalizations in each year was at a similar level of 65.5% in 2018, 62.4% in 2019, and 60% in 2020. The highest incidence was noted in the 0-4 age group at 44.7% of cases in 2018, 42.9% in 2019 and 55.6% in 2020, respectively (all cases of the intestinal form). The predominant species was Y. enterocolitica in both intestinal and extraintestinal forms. The most common serotype was serotype O:3, which was identified in 34 isolates in 2018, 43 isolates in 2019 and 9 isolates in 2020.
CONCLUSIONS: Since 2009, Poland has had a decreasing trend in the incidence of yersiniosis. In 2020, both Poland and Europe saw a sharp decline in the number of cases compared to previous years. This is a result of the occurrence of the COVID-19 pandemic in March 2020, during which many measures were introduced to limit the spread of the SARS-CoV-2 virus, which may also have affected the number of other infections. Although the numbers of cases and incidence of yersiniosis among children under the age of 5 are the highest compared to other age groups, the highest number of hospitalizations was reported in the 10-19 age group, which most likely reflects the decreasing number of laboratory tests ordered on an outpatient basis with age and the significant underreporting of cases in this and older age groups.

The use of antibiotics in aquaculture leads to the proliferation of multidrug-resistant bacteria, and an urgent need for developing new alternatives to prevent and control disease has, thus, arisen. In this scenario, postbiotics represent a promising tool to achieve this purpose; thus, in this study, isolation and selection of bacteria to further produce and evaluate their postbiotics antibacterial activity against fish pathogens was executed. In this respect, bacterial isolates from rainbow trout and Nile tilapia were obtained and tested in vitro against Yersinia ruckeri and Aeromonas salmonicida subsp. salmonicida. From 369 obtained isolates, 69 were selected after initial evaluation. Afterwards, additional screening was carried out by spot-on-lawn assay to finally select twelve isolates; four were identified as Pediococcus acidilactici, seven as Weissella cibaria, and one as Weissella paramesenteroides by matrix assisted laser desorption/ionization, time-of-flight mass spectrometry (MALDI-TOF MS). Selected bacteria were used to obtain postbiotic products to test their antagonistic activity through coculture challenge and broth microdilution assays. The influence of incubation time prior to postbiotic production on antagonistic behavior was also recorded. Two isolates identified as W. cibaria were able to significantly reduce (p < 0.05) A. salmonicida subsp. salmonicida\'s growth in the coculture challenge up to 4.49 ± 0.05 Log CFU/mL, and even though the reduction in Y. ruckeri was not as effective, some inhibition on the pathogen\'s growth was reported; at the same time, most of the postbiotic products obtained showed more antibacterial activity when obtained from broth cultures incubated for 72 h. Based on the results obtained, the preliminary identification of the isolates that expressed the highest inhibitory activity was confirmed by partial sequencing as W. cibaria. Through our study, it can be concluded that postbiotics produced by these strains are useful to inhibit the growth of the pathogens and could, thereby, be applicable in further research to develop suitable tools as feed additives for disease control and prevention in aquaculture.

Diseases are the most significant challenge in the development and stability of aquaculture. In this study, the immunogenic efficiency of polyvalent streptococcosis/lactococcosis and yersiniosis vaccines was evaluated by injection and immersion methods in rainbow trout.. The 450 fish with an average weight of 50 ± 5 g were divided into three treatments and three replications as follows: injection vaccine treatment, immersion vaccine treatment and control group without vaccine administration. Fish were kept for 74 days and sampling was done on days 20, 40 and 60. Then, from the 60th to the 74th day, the immunized groups were challenged with three bacteria Streptococcus iniae (S. iniae), Lactococcus garvieae (L. garvieae) and Yersinia ruckeri (Y. ruckeri) separately. A significant difference was observed in the weight gained (WG) in the immunized groups compared to the control group (P < 0.05). The relative survival percentage (RPS) after 14 days of challenge with S. iniae, L. garvieae and Y. ruckeri in the injection group compared to the control group increased respectively (60%, 60% and 70%), (P < 0.05). Also, RPS in the immersion group had an increase respectively (30%, 40% and 50%) after the challenge with S. iniae, L.garvieae and Y. ruckeri compared to the control group. Immune indicators such as antibody titer, complement and lysozyme activity significantly increased in comparison to the control group (P < 0.05). In general, it can be concluded that applying three vaccines by injection and immersion method has significant effects on immune protection and survival rate. However, the injection method is more effective and more suitable than the immersion method.