Detection of chromosomal and plasmid--encoded virulence determinants in Yersinia enterocolitica and other Yersinia spp. isolated from food animals in Greece

Yersinia enterocolitica Bacteremia Associated with a Ruptured Abdominal Aortic Aneurysm: A Case Report with Literature Review

Yersinia enterocolitica is a foodborne pathogen, mainly associated with disorders involving the gastrointestinal tract, including diarrhea, ileitis, and mesenteric lymphadenitis. Extraintestinal presentation is uncommon in healthy individuals, but bacteremia is reported in immunocompromised hosts. We present a 74-year-old male with Y. enterocolitica serogroup O:3 bacteremia who complicated to rupture of an abdominal aortic aneurysm. With the current case report, we aimed to emphasize the association of Y. enterocolitica bacteremia with abdominal aortic aneurysm rupture. Better surveillance is needed, not only to reduce morbidity and mortality but also to update current epidemiological data on the incidence of such associations.

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.

Antimicrobial resistance of Yersinia enterocolitica and presence of plasmid pYV virulence genes in human and animal isolates

Interactions between bacterial virulence and antimicrobial resistance are of increasing interest in clinical microbiology. On this account, antimicrobial resistance of Yersinia enterocolitica O:3 strains isolated from humans (n = 55), food-chain animals (n = 58) and companion animals (n = 13) was determined in relation to the absence or presence of the pYV plasmid-encoded virulence genes yadA and virF. There were no statistically significant associations between the rate of antimicrobial resistance and the presence or absence of the plasmid, in either human-derived or animal-derived strains. Therefore, it can be concluded that response to conventionally used antimicrobials in Y. enterocolitica O:3 strains is not dependent on pYV-encoded virulence determinants.

Campylobacteriosis, Salmonellosis, Yersiniosis, and Listeriosis as Zoonotic Foodborne Diseases: A Review

Zoonoses are diseases transmitted from animals to humans, posing a great threat to the health and life of people all over the world. According to WHO estimations, 600 million cases of diseases caused by contaminated food were noted in 2010, including almost 350 million caused by pathogenic bacteria. Campylobacter, Salmonella, as well as Yersinia enterocolitica and Listeria monocytogenes may dwell in livestock (poultry, cattle, and swine) but are also found in wild animals, pets, fish, and rodents. Animals, often being asymptomatic carriers of pathogens, excrete them with faeces, thus delivering them to the environment. Therefore, pathogens may invade new individuals, as well as reside on vegetables and fruits. Pathogenic bacteria also penetrate food production areas and may remain there in the form of a biofilm covering the surfaces of machines and equipment. A common occurrence of microbes in food products, as well as their improper or careless processing, leads to common poisonings. Symptoms of foodborne infections may be mild, sometimes flu-like, but they also may be accompanied by severe complications, some even fatal. The aim of the paper is to summarize and provide information on campylobacteriosis, salmonellosis, yersiniosis, and listeriosis and the aetiological factors of those diseases, along with the general characteristics of pathogens, virulence factors, and reservoirs.

Faecal shedding of pathogenic Yersinia enterocolitica determined by qPCR for yst virulence gene is associated with reduced live weight but not diarrhoea in prime lambs

Associations between faecal shedding of pathogenic Yersinia enterocolitica (based on the yst virulence gene) with growth, carcass weight and diarrhoea were investigated using an observational longitudinal study of 1200 crossbred prime (meat) lambs on eight Australian farms. Live weight, breech faecal soiling score (scale 1-5) and faecal consistency score (FCS; scale 1-5) were recorded, and faecal samples collected from each lamb on three sampling occasions; weaning (≈12 weeks of age), post-weaning (≈19 weeks) and pre-slaughter (≈29 weeks). Hot standard carcass weight was measured at slaughter. Faecal samples were screened for presence and concentration of pathogenic Y. enterocolitica using quantitative PCR. Associations of pathogenic Y. enterocolitica detection and shedding intensity with lamb health and production were assessed using general linear models (carcass weight), linear mixed effects models (live weight, FCS and breech soiling score) and non-parametric tests (FCS and breech soiling score). Prevalence for non-pelleted faeces (FCS ≥ 3.0) and diarrhoea (FCS ≥ 4.0) were compared with the two-tailed z-test, odds ratios and relative risk. Lambs shedding pathogenic Y. enterocolitica were 3.78 kg lighter post-weaning (P < 0.001) and 2.61 kg lighter pre-slaughter (P = 0.035) compared to lambs in which pathogenic Y. enterocolitica was not detected. Higher faecal concentration of pathogenic Y. enterocolitica was associated with lower live weight (P < 0.001). There was no association between pathogenic Y. enterocolitica detection and carcass weight. Overall, there was no evidence of association between pathogenic Y. enterocolitica detection and diarrhoea (higher FCS, higher risk for non-pelleted faeces or diarrhoea, or higher breech soiling score). Only one flock had increased relative risk for non-pelleted faeces associated with pathogenic Y. enterocolitica detection, and one other flock had increased relative risk for diarrhoea associated with pathogenic Y. enterocolitica detection. This is the first report of an association between reduced sheep live weight and pathogenic Y. enterocolitica based on the presence of the yst gene for heat stable enterotoxin determined by qPCR in sheep. Notably, impacts on live weight were observed in the absence of diarrhoea.

Evaluation of the pathogenic potential, antimicrobial susceptibility, and genomic relations of Yersinia enterocolitica strains from food and human origin

Yersinia enterocolitica is a food-borne pathogen that causes gastroenteritis with occasional postinfection sequels. This study was aimed to determinate the pathogenic potential, antimicrobial susceptibility, and genomic relationships of Y. enterocolitica strains of different bioserotypes (B/O) isolated from foods and human samples in San Luis, Argentina. Strains obtained by culture were bioserotyped and characterized by phenotypic and genotypic virulence markers, antimicrobial susceptibility, and pulsed-field gel electrophoresis (PFGE). Yersinia enterocolitica was detected in 9.2% of 380 samples, with a distribution of 10.6% (30/284) for food products and 5.2% (5/96) for human samples. Regarding the pathogenic potential, B1A strains of different serotypes were virF(-) ail(-), of which 72.0% (13/18) were ystB(+) with virulence-related phenotypic characteristics. Among B2/O:9 isolates, 75.0% (9/12) exhibited the genotype virF(+) ail(+) ystB(-) along with phenotypic traits associated with virulence; the same genotype was observed in 80.0% (4/5) of B3/O:3 and B3/O:5 strains. By PFGE, it was possible to separate Y. enterocolitica biotypes into 4 clonal groups (A to D) with 23 genomic types, generating a discriminatory index of 0.96. All isolates were susceptible to antimicrobials used for clinical treatment. This study highlights the presence of pathogenic bioserotypes and the high genomic diversity of the Y. enterocolitica strains isolated in our region.

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.

Behavior of Yersinia enterocolitica in Foods

Yersinia enterocolitica are ubiquitous, being isolated frequently from soil, water, animals, and a variety of foods. They comprise a biochemically heterogeneous group that can survive and grow at refrigeration temperatures. The ability to propagate at refrigeration temperatures is of considerable significance in food hygiene. Virulent strains of Yersinia invade mammalian cells such as HeLa cells in tissue culture. Two chromosomal genes, inv and ail, were identified for cell invasion of mammalian. The pathogen can cause diarrhoea, appendicitis and post-infection arthritis may occur in a small proportion of cases. The most common transmission route of pathogenic Y. enterocolitica is thought to be fecal-oral via contaminated food. Direct person-to-person contact is rare. Occasionally, pathogenic Y. enterocolitica has been detected in vegetables and environmental water; thus, vegetables and untreated water are also potential sources of human yersiniosis. However, the isolation rates of pathogenic Y. enterocolitica have been low, which may be due to the limited sensitivity of the detection methods. To identify other possible transmission vehicles, different food items should be studied more extensively. Many factors related to the epidemiology of Y. enterocolitica, such as sources, transmission routes, and predominating genotypes remain obscure because of the low sensitivity of detection methods.

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.

A Selective Chromogenic Plate, YECA, for the Detection of Pathogenic Yersinia enterocolitica: Specificity, Sensitivity, and Capacity to Detect Pathogenic Y. enterocolitica from Pig Tonsils

A new selective chromogenic plate, YECA, was tested for its specificity, sensitivity, and accuracy to detect pathogenic Y. enterocolitica from pig tonsils. We tested a panel of 26 bacterial strains on YECA and compared it to PCA, CIN, and YeCM media. Detection of pathogenic Y. enterocolitica was carried out on 50 pig tonsils collected in one slaughter house. Enrichment was done in PSB and ITC broths. Streaking on YECA and CIN was done in direct, after 24H incubation of ITC, after 48H incubation of PSB and ITC. All the plates were incubated at 30°C during 24 hours. Presence of typical colonies on CIN and YECA was checked, and isolates were biotyped. Pathogenic Y. enterocolitica strains showed an important growth on YECA with small and red fuchsia colonies while biotype 1A exhibited very few violet colonies. Enrichment in ITC during 48H gave the best performance for detecting positive samples in pathogenic Y. enterocolitica, and YECA could detect directly pathogenic Y. enterocolitica strains (2, 3, and 4). Use of YECA in combination with ITC generates a time-saver by giving a positive test in 72H.

Comparison of broth microdilution and disk diffusion test for antimicrobial resistance testing in Yersinia enterocolitica 4/O:3 strains

The aim of this study was to compare the results obtained from two methods for the determination of antimicrobial resistance in 110 Yersinia enterocolitica 4/O:3 strains. Ten antimicrobial agents were tested using broth microdilution and disk diffusion. Similar results were determined for six antimicrobials. Very major errors (false-susceptible by disk diffusion test) were detected for ampicillin (at a rate of 1.8%). Major errors (false-resistant by disk diffusion test) were found for streptomycin (0.9%) and sulfamethoxazole (1.8%). Minor errors (intermediate susceptible by disk diffusion and resistant or susceptible by microdilution) were obtained for ampicillin (2.7%) and sulfamethoxazole (13.6%). All Y. enterocolitica were resistant to at least one antimicrobial agent. Resistances to three classes of antimicrobial agents were obtained by 3% of the strains included in the study. A slightly higher frequency of multiresistance was obtained by disk diffusion (3%) compared with broth microdilution (1%). Resistance to streptomycin was found frequently (13%); in contrast, resistance to tetracycline was rare (1%). The disk diffusion test produced unacceptably high rates of very major errors for ampicillin and a high frequency of minor errors for sulfamethoxazole. Susceptibility tests should thus be carried out by the more reliable method of microdilution. Most of the antimicrobials that can be used for therapy were very effective when tested against Y. enterocolitica. In order to identify changes in susceptibilities as early as possible, antimicrobial resistance in Y. enterocolitica should be regularly surveyed.

Detection, semiquantitative enumeration, and antimicrobial susceptibility of Yersinia enterocolitica in pork and chicken meats in Italy

Yersinia enterocolitica is recognized as an etiological agent of gastroenteritis, lymphadenitis, and chronic sequelae. During 2006 and 2007, 205 samples (125 pork and 80 chicken meats) were collected in Italy and tested for detection and most-probable-number (MPN) enumeration of Y. enterocolitica organisms. The microorganism was isolated from 45 samples (21.9%): 19 (15.2%) pork samples and 26 (32.5%) chicken samples. Y. enterocolitica MPN contamination levels were low, ranging from 0.30 to 1.50/g. Most (94.4%) Y. enterocolitica strains were biotype 1A (serotypes O:3; O:5; O:6,30; O:6,30-6,31; O:7,8-8-8,19; O:8; O:9; O:25,35; O:36; and O nontypeable), and 5.6% of the isolates were bioserotype 2/O:9. All isolates were tested for yadA, ail, inv, ystA, and ystB virulence sequences. The yadA gene was detected in two strains (3.7%) isolated from chicken samples: one Y. enterocolitica 2/O:9 yadA+ ail+ ystA+, and one Y. enterocolitica 1A/O:7,8-8-8,19 yadA+ inv+ ystB+. Two (3.7%) 2/O:9 strains, isolated from pork products, were ail+ ystA+. Most biotype 1A strains were ystB+ (84.3%) and inv+ (39.2%). All strains were sensitive to cefotaxime, ciprofloxacin, chloramphenicol, nalidixic acid, streptomycin, sulfonamide, tetracycline, trimethoprim, and trimethoprim-sulfamethoxazole. Resistance to gentamicin and aztreonam was observed in 1.9% of the isolates. High levels of resistance were detected toward amoxicillin-clavulanic acid (27.8%), ampicillin (75.9%), and erythromycin (100%). The authors hypothesize that Y. enterocolitica pathogenic biotypes are rather uncommon in foods when compared with their isolation rates from animal sources and that chicken meat could be contaminated as well as pig meat and its derived products.

A simplified method for detecting pathogenic Yersinia enterocolitica in slaughtered pig tonsils

The aim of this study was to collect preliminary data on the carriage of pathogenic Yersinia enterocolitica in slaughtered pigs in France and to test a simplified method for detecting these strains from tonsils. From January to March 2009, 900 tonsil swabs were taken from pigs at one slaughterhouse in Brittany, France. The swabs were vortexed in 10 ml PSB broth, then 1 ml was added to 9 ml ITC broth. The media were incubated for 48 h at 25°C. The PSB enrichment broth was streaked on CIN plates and the ITC enrichment broth on SSDC plates. In addition to the ISO 10273 method, we also streaked ITC enrichment broth on CIN plates. The plates were incubated for 24h at 30°C, and we then streaked a maximum of four typical colonies per plate onto a plate containing chromogenic medium (YeCM), for the isolation of pathogenic Y. enterocolitica isolates. In parallel, biochemical assays were carried out to confirm the identification of the isolates as Yersinia and to determine biotype. After passage on a YeCM plate and biochemical tests, 380 strains were confirmed to be pathogenic Y. enterocolitica. Finally, with the ISO 10273 method, 9.1% (CI(95%) [5.8-12.4]) of tonsil swabs and 60% (CI(95%) [45.4-74.6]) of the batches were positive. With the ITC-CIN method, 14.0% (CI95% [10.7-17.3]) of the tonsil swabs and 68.9% (CI(95%) [54.3-83.5]) of the batches were positive. Identification as pathogenic Y. enterocolitica was confirmed for 97.0% of the typical colonies obtained on the chromogenic medium, YeCM. The most prevalent biotype was biotype 4 (80.5% of the isolates), followed by biotype 3. This study demonstrates that the ITC-CIN method, followed by streaking on YeCM, may be an effective approach to the isolation of pathogenic Y. enterocolitica from tonsil swabs and the recovery of positive samples. This method is less time-consuming than the ISO 10273 method and reduces the number of biochemical tests required for the confirmation of Yersinia identification, through the use of YeCM.

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

The prevalence of Yersinia enterocolitica and Yersinia pseudotuberculosis was determined in slaughter pigs from 47 farms in Latvia. Tonsils from 404 pigs representing farms from four geographical areas (Kurzeme, Latgale, Vidzeme, and Zemgale) were collected at slaughter in 2007 and 2008. The prevalences of Y. enterocolitica and Y. pseudotuberculosis were 35 and 3%, respectively. All Y. enterocolitica isolates belonged to bioserotype 4/O:3. Y. enterocolitica was recovered from 35 of 47 pig farms, and Y. pseudotuberculosis was found on 6 farms. The prevalence of Yersinia was highest in Latgale (90%) followed by Kurzeme (39%), Zemgale (33%), and Vidzeme (21%). Y. enterocolitica 4/O:3 was sensitive to amoxicillin-clavulanic acid, aztreonam, cefotaxime, ceftriaxone, chloramphenicol, ciprofloxacin, nalidixic acid, trimethoprim, and trimethoprim-sulfamethoxazole and resistant to ampicillin, cephalothin, erythromycin, streptomycin, sulfamethoxazole, and tetracycline. Y. pseudotuberculosis exhibited resistance to erythromycin and sulfamethoxazole but not to the other antimicrobial agents tested. The results of this study are a valuable starting point for monitoring the prevalence and antimicrobial resistance of Yersinia in pigs in Latvia.

Variation in the prevalence of enteropathogenic Yersinia in slaughter pigs from Belgium, Italy, and Spain

Tonsils of 829 fattening pigs originating from Belgium (n = 201), Italy (n = 428), and Spain (n = 200) were collected between 2005 and 2007 to study the prevalence of enteropathogenic Yersinia in slaughter pigs. Isolation of Yersinia enterocolitica and Yersinia pseudotuberculosis was done by selective enrichment and by cold enrichment for 7 and 14 days. Pathogenic Y. enterocolitica and Y. pseudotuberculosis isolates were identified by polymerase chain reaction targeting the chromosomal genes ail and inv, respectively, as well as the plasmid-encoded virF of both species. A significantly higher (p < 0.001) prevalence of ail-positive Y. enterocolitica in Spain (93%) than in Belgium (44%) or Italy (32%) was observed. virF-positive Y. enterocolitica was present in 77% of ail-positive samples. Bioserotype 4/O:3 was the most common type in all three countries. Bioserotypes 2/O:5 and 3/O:9 were found in Italy (1%) and Belgium (9%), respectively. The prevalence of inv- and virF-positive Y. pseudotuberculosis was 2% and 1% in Belgium and Italy, respectively. Y. pseudotuberculosis was not detected in pigs from Spain. Bioserotypes 1/O:1 (20%), 1/O:2 (20%), and 2/O:3 (60%) were found in Belgium, and 1/O:1 (60%) and 2/O:3 (20%) in Italy. The most efficient method for isolation of Y. enterocolitica was combined cold enrichment for 7 and 14 days; however, the isolation method for Y. pseudotuberculosis was cold enrichment for 14 days. Fattening pigs seem to be an important reservoir of pathogenic Y. enterocolitica in Belgium, Italy, and Spain. Bioserotype 4/O:3 of Y. enterocolitica and bioserotypes 2/O:3 and 1/O:1 of Y. pseudotuberculosis have been shown to predominate.

Application of loop-mediated isothermal amplification for detection of Yersinia enterocolitica in pork meat

A loop-mediated isothermal amplification (LAMP) method was developed for the detection of Yersinia enterocolitica isolates in both pure bacterial cultures and pork meat. The LAMP primers, which corresponded to the gyrB gene, accurately identified 4 different bioserotypes of Y. enterocolitica. These primers failed to detect Y. pseudotuberculosis, Y. frederiksenii, and 17 non-Yersinia strains. The sensitivity of the LAMP assay for the detection of Y. enterocolitica in pure culture was 65 CFU/mL (31.6 fg of genomic DNA). The LAMP assay was conducted for the detection of Y. enterocolitica strains in 21 pig tonsil samples and 73 pork meat samples obtained from 94 slaughtered pigs belonging to 4 different herds. Y. enterocolitica was found to be present in 4 tonsil samples and none in meat samples. This is the first report in which the LAMP assay was employed for the detection of Y. enterocolitica in food samples.

Bacterial conjugation in the cytoplasm of mouse cells

Intracellular pathogenic organisms such as salmonellae and shigellae are able to evade the effects of many antibiotics because the drugs are not able to penetrate the plasma membrane. In addition, these bacteria may be able to transfer genes within cells while protected from the action of drugs. The primary mode by which virulence and antibiotic resistance genes are spread is bacterial conjugation. Salmonellae have been shown to be competent for conjugation in the vacuoles of cultured mammalian cells. We now show that the conjugation machinery is also functional in the mammalian cytosol. Specially constructed Escherichia coli strains expressing Shigella flexneri plasmid and chromosomal virulence factors for escape from vacuoles and synthesizing the invasin protein from Yersinia pseudotuberculosis to enhance cellular entry were able to enter 3T3 cells and escape from the phagocytic vacuole. One bacterial strain (the donor) of each pair to be introduced sequentially into mammalian cells had a conjugative plasmid. We found that this plasmid could be transferred at high frequency. Conjugation in the cytoplasm of cells may well be a general phenomenon.

Distribution of virF/lcrF-positive Yersinia pseudotuberculosis serotype O:3 at farm level

The distribution and persistence of pathogenic, virF/lcrF-positive Yersinia pseudotuberculosis were investigated in pigs and in the pig house environment during rearing to determine possible contamination routes of early infections. Based on Y. pseudotuberculosis-positive tonsils of slaughter pigs in our previous study, Y. pseudotuberculosis-positive animals were traced back to the farms. Eight farms were visited from 6-10 months later, and a total of 155 pooled and six individual faecal samples from pigs and 116 pooled environmental samples were collected for analysis by different culture methods. Four of the eight farms were found to be Y. pseudotuberculosis-positive. All positive faecal samples were obtained from fattening pigs, with prevalence varying from 5% to 71% on positive farms. Sows, boars and suckling piglets were Y. pseudotuberculosis-negative on all farms. Most Y. pseudotuberculosis-positive farms (three of four) were on a one-site production system, which had a higher prevalence of Y. pseudotuberculosis (5-26%) among fattening pigs than the all-in, all-out system (1-5%). All Y. pseudotuberculosis isolates belonged to serotype O:3 and carried the virF/lcrF gene on the virulence plasmid. Biotypes 2 and 3 were involved, the latter in one isolate and not being previously reported in pigs. Altogether 53 isolates from 16 positive samples were characterized with pulsed-field gel electrophoresis (PFGE). Using SpeI, NotI and XbaI enzymes, four, three and two different PFGE patterns were obtained respectively. A total of nine different genotypes were identified when the profiles of the enzymes were combined. The most common genotypes were gIV, found on three, and gXII, found on two of the four Y. pseudotuberculosis-positive farms. The same genotypes previously detected in pig tonsils were present in pig faeces from the same farm, indicating that some Y. pseudotuberculosis strains can persist in the pig house environment.