Prevalence and antimicrobial resistance of Yersinia enterocolitica and Yersinia pseudotuberculosis in slaughter pigs in Latvia

Higher Resistance of Yersinia enterocolitica in Comparison to Yersinia pseudotuberculosis to Antibiotics and Cinnamon, Oregano and Thyme Essential Oils

Yersiniosis is an important zoonotic disease; however, data are scarce on the resistance of enteropathogenic yersiniae, especially that of Y. pseudotuberculosis. Minimum inhibitory concentrations (MIC) of 21 antibiotics and 3 essential oils (EOs) were determined by broth microdilution for Y. enterocolitica bioserotype 4/O:3 strains isolated from domestic swine (n = 132) and Y. pseudotuberculosis strains isolated from wild boars (n = 46). For 15 of 21 antibiotics, statistically significant differences were found between MIC values of Y. enterocolitica and Y. pseudotuberculosis. While Y. enterocolitica was more resistant to amoxiclav, ampicillin, cefotaxime, cefuroxime, gentamicin, imipenem, meropenem, tetracycline, tobramycin, and trimethoprim, Y. pseudotuberculosis was more resistant to cefepime, ceftazidime, colistin, erythromycin, and nitrofurantoin. Statistically significant differences were found between various essential oils (p < 0.001) and species (p < 0.001). The lowest MICs for multiresistant Y. enterocolitica (n = 12) and Y. pseudotuberculosis (n = 12) were obtained for cinnamon (median 414 and 207 μg/mL, respectively) and oregano EOs (median 379 and 284 μg/mL), whereas thyme EO showed significantly higher MIC values (median 738 and 553 μg/mL; p < 0.001). There was no difference between Y. enterocolitica strains of plant (1A) and animal (4/O:3) origin (p = 0.855). The results show that Y. enterocolitica is generally more resistant to antimicrobials than Y. pseudotuberculosis.

Prevalence and Persistence of Multidrug-Resistant Yersinia enterocolitica 4/O:3 in Tonsils of Slaughter Pigs from Different Housing Systems in Croatia

Yersinia enterocolitica is one of the priority biological hazards in pork inspection. Persistence of the pathogen, including strains resistant to antimicrobials, should be evaluated in pigs from different housing systems for risk ranking of farms. In this 2019 study, tonsils were collected from 234 pigs, of which 69 (29.5%) were fattened on 3 big integrated farms, 130 (55.5%) on 10 medium-sized farms, and 35 (15%) on 13 small family farms. In addition, 92 pork cuts and minced meat samples from the same farms were tested for the presence of Y. enterocolitica using the culture method. Phenotypic and genetic characteristics of the isolates were compared with previously collected isolates from 2014. The overall prevalence of Y. enterocolitica in pig tonsils was 43% [95% CI 36.7−49.7]. In pigs from big integrated, medium-sized, and small family farms, the prevalence was 29%, 52%, and 40%, respectively. All retail samples of portioned and minced pork tested negative for pathogenic Y. enterocolitica, likely due to high hygienic standards in slaughterhouses/cutting meat or low sensitivity of culture methods in these matrices. The highest recovery rate of the pathogen from tonsils was found when alkali-treated PSB and CIN agar were combined. The biosecurity category of integrated and medium farms did not affect the differences in prevalence of Y. enterocolitica (p > 0.05), in contrast to family farms. Pathogenic ail-positive Y. enterocolitica biotype 4 serotype O:3 persisted in the tonsils of pigs regardless of the type of farm, slaughterhouse, and year of isolation 2014 and 2019. PFGE typing revealed the high genetic concordance (80.6 to 100%) of all the Y. enterocolitica 4/O:3 isolates. A statistically significant higher prevalence of multidrug-resistant Y. enterocolitica 4/O:3 isolates was detected in the tonsils of pigs from big integrated farms compared to the other farm types (p < 0.05), with predominant and increasing resistance to nalidixic acid, chloramphenicol, and streptomycin. This study demonstrated multidrug resistance of the pathogen in pigs likely due to more antimicrobial pressure on big farms, with intriguing resistance to some clinically relevant antimicrobials used in the treatment of yersiniosis in humans.

Prudent Antimicrobial Use Is Essential to Prevent the Emergence of Antimicrobial Resistance in Yersinia enterocolitica 4/O:3 Strains in Pigs

Yersinia enterocolitica is a psychrotrophic zoonotic foodborne pathogen. Pigs are considered the main reservoir of Y. enterocolitica 4/O:3, which is the most commonly isolated bioserotype in many European countries. Consuming pork contaminated with Y. enterocolitica can be a health threat, and antimicrobial-resistant strains may complicate the treatment of the most severe forms of yersiniosis. We analyzed the antimicrobial resistance of 1,016 pathogenic porcine Y. enterocolitica 4/O:3 strains originating from Belgium, Estonia, Finland, Germany, Italy, Latvia, Russia, Spain, and the United Kingdom. Based on available reports, we also compared antimicrobial sales for food production animals in these countries, excluding Russia. Antimicrobial resistance profiles were determined using a broth microdilution method with VetMIC plates for 13 antimicrobial agents: ampicillin, cefotaxime, ceftiofur (CTF), chloramphenicol (CHL), ciprofloxacin, florfenicol, gentamicin, kanamycin, nalidixic acid (NAL), streptomycin (STR), sulfamethoxazole (SME), tetracycline (TET), and trimethoprim (TMP). The antimicrobial resistance of Y. enterocolitica 4/O:3 strains varied widely between the countries. Strains resistant to antimicrobial agents other than ampicillin were rare in Estonia, Finland, Latvia, and Russia, with prevalence of 0.7, 0.4, 0, and 8.3%, respectively. The highest prevalence of antimicrobial resistance was found in Spanish and Italian strains, with 98 and 61% of the strains being resistant to at least two antimicrobial agents, respectively. Resistance to at least four antimicrobial agents was found in 34% of Spanish, 19% of Italian, and 7.1% of English strains. Antimicrobial resistance was more common in countries where the total sales of antimicrobials for food production animals are high and orally administered medications are common. Our results indicate that antimicrobials should be used responsibly to treat infections, and parenteral medications should be preferred to orally administered mass medications.

Prevalence, Virulence and Antimicrobial Susceptibility of Salmonella spp., Yersinia enterocolitica and Listeria monocytogenes in European Wild Boar (Sus scrofa) Hunted in Tuscany (Central Italy)

Wild boar is an animal the population of which constantly increases in Europe. This animal plays an important role as a reservoir for several pathogens, including three of the most important zoonoses: salmonellosis, yersiniosis and listeriosis. The aim of this investigation was to evaluate the occurrence of antimicrobial-resistant and virulence factor genes of Salmonella spp., Yersinia enterocolitica and Listeria monocytogenes isolated from wild boar in Tuscany (Central Italy). During two consequent hunting seasons (2018/2019 and 2019/2020), rectal swabs, spleens and livers were collected from 287 hunted wild boar to isolate strains. Each isolate was tested to investigate its antimicrobial resistance and to detect virulence factor genes by PCR. Eighteen Salmonella strains (6.27%) were isolated. Of these, 66.7% were resistant to streptomycin, 13.4% to cephalothin, 6.67% to imipenem and one isolate (6.67%) was resistant simultaneously to five antimicrobials. Moreover, the most detected genes were sopE (73.4%), pipB (66.7%), sodCI (53.3%), spvR and spvC (46.7%). In total, 54 (17.8%) Yersinia enterocolitica were isolated; of them, 26 (48.1%), 9 (16.7%), 17 (31.5%), 1 (1.85%) and 1 (1.85%) belonged to biotypes 1, 2, 3, 4 and 5, respectively. All strains (100%) demonstrated resistance to cephalothin and 70.4% to amoxicillin-clavulanic acid, 55.6% to ampicillin, and 37.0% to cefoxitin. Additionally, the most detected genes were ystA (25.9%), inv (24.1%), ail (22.2%), ystB (18.5%) and virF (14.8%). Finally, only one Listeriamonocytogenes isolate (0.35%) was obtained, belonging to serogroup IVb, serovar 4b, and it was found to be resistant to cefoxitin, cefotaxime and nalidixic acid. The results highlighted the role of wild boar as a carrier for pathogenic and antimicrobial-resistant Salmonella spp., Yersinia enterocolitica and Listeria monocytogens, representing a possible reservoir for domestic animals and human pathogens.

Pan-genomics, drug candidate mining and ADMET profiling of natural product inhibitors screened against Yersinia pseudotuberculosis

Yersinia pseudotuberculosis belongs to the family Enterobacteriaceae and is responsible for scarlatinoid fever, food poisoning, post-infectious complications like erythema nodosum/reactive arthritis as well as pseudoappendicitis in children. Genome sequences of the 23 whole genomes from NCBI were utilized for conducting the pan-genomic analysis. Essential proteins from the core region were obtained and drug targets were identified using a hierarchal in silico approach. Among these, multidrug resistance protein sub-unit mdtC was chosen for further analysis. This protein unit confers resistance to antibiotics upon forming a tripartite complex with units A and B in Escherichia coli. Details of the function have not yet been elucidated experimentally in Yersinia spp. Computational structure modeling and validation were followed by screening against phytochemical libraries of traditional Indian (Ayurveda), North African, and traditional Chinese flora using Molecular Operating Environment software version 2019.0102. ADMET profiling and descriptor study of best docked compounds was studied. Since phytotherapy is the best resort to antibiotic resistance so these compounds should be tested experimentally to further validate the results. The obtained information could aid wet-lab scientists to work on the scaffold of screened drug-like compounds from natural resources. This could be useful in our quest for antibiotic-resistant therapy against Y. pseudotuberculosis.

Development of a novel multiplexed qPCR and Pyrosequencing method for the detection of human pathogenic yersiniae

The purpose of this study was to develop a novel and robust molecular assay for the detection of human pathogenic yersiniae (i.e. Yersinia enterocolitica, Y. pseudotuberculosis and Y. pestis) in complex food samples. The assay combines multiplexed real-time PCR (qPCR) and Pyrosequencing for detecting and differentiating human pathogenic yersiniae with high confidence through sequence based confirmation. The assay demonstrated 100% specificity and inclusivity when tested against a panel of 14 Y. enterocolitica, 22 Y. pestis, 24 Y. pseudotuberculosis and a diverse selection of 17 other non-Yersinia bacteria. Pyrosequencing reads ranged from 28 to 40bp in length and had 94-100% sequence identity to the correct species in the GenBank nr database. Microbial enrichments of 48 ready-to-eat foods collected in the Greater Toronto Area from March 2014 to May 2014, including 46 fresh sprout and 2 salad products, were then tested using the assay. All samples were negative for Y. pestis and Y. pseudotuberculosis. Both salads (n=2) and 35% of sprout products (n=46) including 7.1% of alfalfa sprouts (n=14), 81% of bean sprouts (n=16), 12% of mixed sprouts (n=8) tested positive for Y. enterocolitica which was not detected in broccoli sprouts (n=5), onion sprouts (n=1), and pea sprouts (n=2). Cycle thresholds (Ct) of positive samples for Y. enterocolitica were between 23.0 and 37.9 suggesting post enrichment concentrations of approximately 1×10² to 1×10⁶Y. enterocolitica per 1mL of enriched broth. An internal amplification control which was coamplified with targets revealed PCR inhibition in five samples which was resolved following a one in ten dilution. Pyrosequencing of qPCR amplicons suggests monoclonality and revealed a single nucleotide polymorphism that is present in Y. enterocolitica biotype 1A suggesting low pathogenicity of the detected strains. This study is the first to combine Pyrosequencing and qPCR for the detection of human pathogenic yersiniae and is applicable to a broad range of complex samples including ready-to-eat food samples.

Prevalence of Salmonella spp. and Yersinia enterocolitica in/on tonsils and mandibular lymph nodes of slaughtered pigs

A total of 156 tonsils and 156 mandibular lymph nodes from fattening pigs originating from 13 farms were sampled in Croatian slaughterhouses and examined for Salmonella spp. (n=78 per organ) and Yersinia enterocolitica (n=78 per organ) by cultural methods. Salmonella was isolated from two tonsils only, both originated from animals from the same farm (5.12%), while Y. enterocolitica were recovered from 26 tonsils (33.33%) which could be traced back to 10 farms. Salmonella was absent in mandibular lymph nodes, and Y. enterocolitica was isolated from eight lymph nodes (10.25%) which originated from six farms. Y. enterocolitica was present inside the lymph nodes of two pigs. The high prevalence of Y. enterocolitica in/on pig tonsils could be the result of cross-contamination during splitting the carcasses with head. This procedure may result in higher prevalence of Y. enterocolitica on surface of mandibular lymph nodes than in their depth. Traditional veterinary postmortem examination of pig halves will not necessarily contribute to cross-contamination with Salmonella or Yersinia under conditions of present slaughter practice.

Molecular analysis of β-lactamase genes to understand their differential expression in strains of Yersinia enterocolitica biotype 1A

Beta-lactams are used as major therapeutic agents against a number of infectious agents. Due to widespread use of β-lactams, β-lactamases have evolved at a rapid pace leading to treatment failures. Yersinia enterocolitica causes many gastrointestinal problems. It is an extremely heterogeneous species comprising more than fifty serotypes and six biotypes which differ in their ecological niches, geographical distribution and pathogenic potential. Though biotype 1A strains have been associated with outbreaks of Yersiniosis, there has been a controversy regarding their pathogenicity. The strains of Y. enterocolitica isolated from India belonged to biotype 1A and possessed genes for two β-lactamases namely, blaA and blaB. An earlier study by us reported differential expression of blaA by strains of Y. enterocolitica biotype 1A. The present study has been carried out to understand the molecular bases which regulate the expression of blaA in Y. enterocolitica biotype 1A. We concluded that six types of blaA variants were present in strains of biotype 1A. Neither amino acid substitutions in blaA nor mutations in promoter regions of blaA contributed to differential expression of blaA in Y. enterocolitica biotype 1A. Rather, the secondary structures attained by mRNA of blaA might underlie the differential expression of blaA in Y. enterocolitica.

Detection, enumeration and characterization of Yersinia enterocolitica 4/O:3 in pig tonsils at slaughter in Northern Italy

Tonsils from 150 pigs slaughtered at 270 days or older were tested for Yersinia enterocolitica with different cultural methods. Samples were collected in three different abattoirs of Northern Italy between April and November 2012 and were analysed by direct plating on cefsulodin-irgasan-novobiocin (CIN) agar and by enrichment procedures following the ISO 10273:2003 reference method. Twenty-three (15.3%) samples were positive: 22 tonsils (14.7%) were positive for human pathogenic Y. enterocolitica bio-serotype 4/O:3 and one tonsil (0.7%) for Y. enterocolitica bio-serotype 1A/7,8-8,8,19. Seventeen samples out of 23 (73.9%) were positive by direct plating method. Among the enrichment procedures, the best recovery rate (8 positives out of 23; 34.8%) was obtained by the two-day enrichment in peptone-sorbitol-bile (PSB) broth followed by plating on CIN agar plates. The two-day enrichment in PSB followed by potassium hydroxide (KOH) treatment before plating onto CIN agar gave 7 positives out of 23 (30.4%), decreasing to 3 positives (13.0%) without KOH treatment. The worst results were obtained by prolonged (five days) enrichment in PSB, with or without KOH treatment, followed by plating on CIN agar: 4.3% (1 out of 23) and 0.0% recovery rates, respectively. The mean concentration was 1.9 × 10(4)CFU/g, with a minimum of 1.0 × 10(2)CFU/g and a maximum of 5.8 × 10(4)CFU/g, thus demonstrating that tonsils may play an important role in contamination of pluck sets, carcasses, and slaughterhouse environment. Prevalence of virulence genes among the Y. enterocolitica 4/O:3 isolates was as follows: 12/22 (54.5%) for yadA, 21/22 (95.5%) for ail, 21/22 (95.5%) for inv and 22/22 (100%) for ystA. All Y. enterocolitica 4/O:3 isolates were sensitive to amoxicillin/clavulanic acid, ciprofloxacin and ceftazidime and resistant to ampicillin and cephalotin. High proportions of 4/O:3 isolates (95%) were sensitive to cefotaxime, gentamicin, kanamicin and nalidixic acid. High levels of resistance were observed to sulphonamide compounds (91%), streptomycin (64%) and chloramphenicol (55%). Multi-resistant isolates were very common; resistance to three or more antimicrobials was observed in 91% (20/22) of 4/O:3 isolates. High level of resistance to chloramphenicol was possibly due to coresistance to tiamphenicol, which was detected in 100% of the isolates. XbaI-PFGE detected four clusters among the 22 Y. enterocolitica 4/O:3 isolates. The most represented accounted for 77% (17/22) of the isolates, the second most common was found in 14% (3/22) of the isolates and the two other profiles were observed in single isolates. The comparison with a selection of human isolates supported the role of the pig as reservoir of 4/O:3 Y. enterocolitica.

Within-batch prevalence and quantification of human pathogenic Yersinia enterocolitica and Y. pseudotuberculosis in tonsils of pigs at slaughter

Yersiniosis is a common bacterial zoonosis in Europe and healthy pigs are known to be the primary reservoir of human pathogenic Yersinia enterocolitica and Y. pseudotuberculosis. However, little information is available about the prevalence of these pathogens within pig batches at time of slaughter. The tonsils of 7047 fattening pigs, belonging to 100 farms, were aseptically collected immediately after evisceration in two Belgian slaughterhouses. The batch size varied between 70 and 930 pigs. On average, 70 pigs were sampled per batch. The tonsils were examined by direct plating on cefsulodin-irgasan-novobiocin (CIN) agar plates and the number of suspect Yersinia colonies was counted. Pathogenic Y. enterocolitica serotype O:3 were found in tonsils of 2009 pigs (28.5%), originating from 85 farms. The within-batch prevalence in positive farms ranged from 5.1 to 64.4%. The number of Y. enterocolitica in positive pigs varied between 2.01 and 5.98 log10 CFU g(-1) tonsil, with an average of 4.00 log10 CFU g(-1) tonsil. Y. pseudotuberculosis was found in seven farms, for which the within-batch prevalence varied from 2 to 10%. In five of these farms, both Y. enterocolitica and Y. pseudotuberculosis were simultaneously present. Human pathogenic Yersinia spp. are widespread in slaughter pig batches in Belgium as 87% of the tested batches were infected with these pathogens at the time of slaughter. The large variation of the prevalence between batches may lead to different levels of contamination of carcasses and risks for public health.

Genetic diversity and antimicrobial resistance of Yersinia enterocolitica isolated from pigs and humans in Lithuania

BACKGROUND

Yersiniosis is one of the three leading foodborne zoonoses in Lithuania, and the incidence of 12.86 per 100,000 population was the highest among EU member states in 2010. Contaminated pig carcasses and subsequently undercooked pig meat are considered to be the primary transmission vehicle of enteropathogenic Y. enterocolitica to consumers. With the aim of evaluating pigs as a possible source of human yersiniosis in Lithuania, this study investigated the genetic diversity of Y. enterocolitica isolated from pigs and human cases of yersiniosis. In addition, the antimicrobial resistance of selected isolates from both sources was compared.

RESULTS

In total, 83 Y. enterocolitica strains were characterised using pulsed field gel electrophoresis. Overall, 68% of Y. enterocolitica 4/O:3 pulsotypes found in human clinical samples were identical to 81% of pulsotypes found in the pig production chain. Yersinia enterocolitica pulsotype II was confirmed as the dominant pulsotype in the pig production chain and was identical to nine of 19 Y. enterocolitica strains found in humans. All tested Y. enterocolitica 4/O:3 strains were resistant to ampicillin and erythromycin and sensitive to ciprofloxacin. Of the strains studied, 5% were resistant to tetracycline and streptomycin.

CONCLUSION

This study showed that pigs may be the main source of human yersiniosis in Lithuania. In addition, Y. enterocolitica 4/O:3 strains isolated from the pig production chain and from yersiniosis patients shared similar resistance to different antimicrobials.

Antimicrobial susceptibility and distribution of β-lactamase A (blaA) and β-lactamase B (blaB) genes in enteropathogenic Yersinia species

One hundred eighty-six strains of enteropathogenic Yersinia (Y.) enterocolitica of bioserotypes 2/O:5,27, 2/O:9, 3/O:3, and 4/O:3 and 12 strains of Yersinia pseudotuberculosis of bioserotypes 1/O:1, 1/O:2, and 2/O:1 from different human (feces) and nonhuman (pig, pork, wild boar, monkey, chinchilla, mara, capybara, salad) sources collected in the years 1995-2009 were examined. Antimicrobial resistance patterns for 12 antimicrobial agents were generated using broth microdilution. The presence and characterization of the β-lactamase genes blaA and blaB were studied using polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism (RFLP), respectively. The expression of β-lactamase BlaA and BlaB was detected using double-disc diffusion. Y. enterocolitica strains showed resistance to ampicillin (92%), streptomycin (13%), and sulfamethoxazole (2%). Intermediate susceptibility to tetracycline was shown by two Y. enterocolitica strains. All Y. pseudotuberculosis strains were susceptible to all tested antimicrobial agents. Most (99%) of the Y. enterocolitica strains carried both β-lactamase genes. One strain of bioserotype 3/O:3 lacked both genes. In contrast, all Y. pseudotuberculosis strains carried neither of the β-lactamase genes. Homogeneity was detected in all blaA and blaB genes of Y. enterocolitica using PCR-RFLP. The majority (89%) of Y. enterocolitica strains expressed both β-lactamase enzymes, whereas none of the Y. pseudotuberculosis strains showed expression of either enzyme. Also, it seems that the resistance of Y. enterocolitica has not changed during the last years.