Molecular characterization of Yersinia enterocolitica by pulsed-field gel electrophoresis and hybridization of DNA fragments to ail and pYV probes

Diversity of Yersinia enterocolitica isolated from pigs in a French slaughterhouse over 2 years

The pig is one of the main reservoirs of Yersinia enterocolitica strains pathogenic to humans. A description of the Y. enterocolitica population in this reservoir, and accurate discriminatory techniques for typing isolates are needed for prevention, outbreak investigation, and surveillance. This study investigates the genetic diversity of pathogenic Y. enterocolitica isolates obtained from pig tonsils in a French pig slaughterhouse in 2009 (S1) and 2010 (S2). The use of Pulsed-Field Gel Electrophoresis (PFGE) and MLVA as typing techniques was also compared and evaluated. First, a total of 167 isolates (12 of biotype 3 recovered during S1, and 155 of biotype 4 recovered during S1 and S2) were typed by PFGE using the XbaI enzyme. MLVA was then tested on all the biotype 3 isolates in addition to 70 selected biotype 4 isolates recovered over the 2 years. PFGE generated two specific XbaI-PFGE profiles for biotype 3 isolates. Nine XbaI profiles were obtained for biotype 4, with a higher diversity (ID = 0.599) than biotype 3 (ID = 0.167). Two out of the nine XbaI profiles were reported during both surveys and at different months. MLVA improved the differentiation between isolates; the index of diversity reached 0.621 and 0.958, respectively, for biotype 3 (three MLVA types) and biotype 4 (32 MLVA types). The MLVA types for biotype 4 differed over the two surveys, but some isolates with different MLVA types were genetically closely related. This study provides an initial evaluation of the genetic diversity of Y. enterocolitica strains isolated from pigs in France. We show that some PFGE profiles are maintained in the pig production sector, and, through MLVA, that part of the Y. enterocolitica population remained genetically close over the two years. MLVA proved its effectiveness as a tool for investigating pathogenic Y. enterocolitica strains isolated from pigs.

Molecular epidemiology of Yersinia enterocolitica infections

Yersinia enterocolitica is an important food-borne pathogen that can cause yersiniosis in humans and animals. The epidemiology of Y. enterocolitica infections is complex and remains poorly understood. Most cases of yersiniosis occur sporadically without an apparent source. The main sources of human infection are assumed to be pork and pork products, as pigs are a major reservoir of pathogenic Y. enterocolitica. However, no clear evidence shows that such a transmission route exists. Using PCR, the detection rate of pathogenic Y. enterocolitica in raw pork products is high, which reinforces the assumption that these products are a transmission link between pigs and humans. Several different DNA-based methods have been used to characterize Y. enterocolitica strains. However, the high genetic similarity between strains and the predominating genotypes within the bio- and serotype have limited the benefit of these methods in epidemiological studies. Similar DNA patterns have been obtained among human and pig strains of pathogenic Y. enterocolitica, corroborating the view that pigs are an important source of human yersiniosis. Indistinguishable genotypes have also been found between human strains and dog, cat, sheep and wild rodent strains, indicating that these animals are other possible infection sources for humans.

Genotyping of human and porcine Yersinia enterocolitica, Yersinia intermedia, and Yersinia bercovieri strains from Switzerland by amplified fragment length polymorphism analysis

In this study, 231 strains of Yersinia enterocolitica, 25 strains of Y. intermedia, and 10 strains of Y. bercovieri from human and porcine sources (including reference strains) were analyzed using amplified fragment length polymorphism (AFLP), a whole-genome fingerprinting method for subtyping bacterial isolates. AFLP typing distinguished the different Yersinia species examined. Representatives of Y. enterocolitica biotypes 1A, 1B, 2, 3, and 4 belonged to biotype-related AFLP clusters and were clearly distinguished from each other. Y. enterocolitica biotypes 2, 3, and 4 appeared to be more closely related to each other (83% similarity) than to biotypes 1A (11%) and 1B (47%). Biotype 1A strains exhibited the greatest genetic heterogeneity of the biotypes studied. The biotype 1A genotypes were distributed among four major clusters, each containing strains from both human and porcine sources, confirming the zoonotic potential of this organism. The AFLP technique is a valuable genotypic method for identification and typing of Y. enterocolitica and other Yersinia spp.

Interpretation of Pulsed-Field Gel Electrophoresis Patterns in Foodborne Disease Investigations and Surveillance

Since the establishment of the well-known Tenover criteria in 1995 (Tenover et al., 1995), relatively few papers have been published about the interpretation of subtyping data generated by pulsed-field gel electrophoresis (PFGE). This paper describes the approach that has been used in the PulseNet network during the past 10 years. PFGE data must always be interpreted in the proper epidemiological context and PFGE data can not alone prove an epidemiological connection. The Tenover criteria are not generally applicable to the interpretation of PFGE subtyping data of foodborne pathogens. The reproducibility of the method with a particular organism, the quality of the PFGE gel, the variability of the organism being subtyped, and the prevalence of the pattern in question must always be considered. Only isolates displaying indistinguishable patterns should be included in the detection of clusters of infections or the initial case definition in a point-source outbreak. More variability (patterns differing from each other in two to three band positions) may be accepted if the outbreak has been going on for some time or if person-person spread is a prominent feature. If epidemiological information is sufficiently strong, isolates with markedly different PFGE patterns may be included in an outbreak.

Application of fluorescent amplified fragment length polymorphism for comparison of human and animal isolates of Yersinia enterocolitica

An amplified fragment length polymorphism (AFLP) method, developed to genotype Yersinia enterocolitica, has been used to investigate 70 representative strains isolated from humans, pigs, sheep, and cattle in the United Kingdom. AFLP primarily distinguished Y. enterocolitica strains according to their biotype, with strains dividing into two distinct clusters: cluster A, comprising largely the putatively pathogenic biotypes (BT2 to -4), and cluster B, comprising the putatively nonpathogenic biotype 1A strains and a single BT1B isolate. Within these two clusters, subclusters formed largely on the basis of serotype. However, AFLP profiles also allowed differentiation of strains within these serotype-related subclusters, indicating the high discriminatory power of the technique for Y. enterocolitica. Investigation of the relationship between strain AFLP profile and host confirmed that pigs are, and provides further proof that sheep may be, potential sources of human infection with putatively pathogenic strains. However, the results suggest that some strains causing human disease do not come from veterinary sources identifiable at this time. The distribution of some BT1A isolates within cluster A raises questions about the relationship between virulence potential and biotype.

Identification and characterization of pathogenic Yersinia enterocolitica isolates by PCR and pulsed-field gel electrophoresis

Approximately 550 to 600 yersiniosis patients are reported annually in Sweden. Although pigs are thought to be the main reservoir of food-borne pathogenic Yersinia enterocolitica, the role of pork meat as a vehicle for transmission to humans is still unclear. Pork meat collected from refrigerators and local shops frequented by yersiniosis patients (n=48) were examined for the presence of pathogenic Yersinia spp. A combined culture and PCR method was used for detection, and a multiplex PCR was developed and evaluated as a tool for efficient identification of pathogenic food and patient isolates. The results obtained with the multiplex PCR were compared to phenotypic test results and confirmed by pulsed-field gel electrophoresis (PFGE). In all, 118 pork products (91 raw and 27 ready-to-eat) were collected. Pathogenic Yersinia spp. were detected by PCR in 10% (9 of 91) of the raw pork samples (loin of pork, fillet of pork, pork chop, ham, and minced meat) but in none of the ready-to-eat products. Isolates of Y. enterocolitica bioserotype 4/O:3 were recovered from six of the PCR-positive raw pork samples; all harbored the virulence plasmid. All isolates were recovered from food collected in shops and, thus, none were from the patients' home. When subjected to PFGE, the six isolates displayed four different NotI profiles. The same four NotI profiles were also present among isolates recovered from the yersiniosis patients. The application of a multiplex PCR was shown to be an efficient tool for identification of pathogenic Y. enterocolitica isolates in naturally contaminated raw pork.

Molecular heterogeneity inYersinia enterocoliticaand ‘Y. enterocolitica-like’ species – Implications for epidemiology, typing and taxonomy

Yersinia enterocolitica is an extremely heterogeneous species. Serotyping and biotyping have been used extensively, in the past, to study its heterogeneity and epidemiology. Application of methods like ribotyping, pulsed-field gel electrophoresis and a host of other genomic techniques have further revealed molecular heterogeneity in this species. Furthermore, these methods may be used effectively to supplement serotyping and biotyping schema for studying epidemiology of Y. enterocolitica. This is evident from the ability of some of these methods to subtype strains belonging to serogroups O:3, O:9 and O:8 - which are most commonly encountered in human Yersiniosis. Multilocus enzyme electrophoresis and nucleotide sequencing have reiterated the taxonomic relationships of this organism. However there is paucity of information about the molecular heterogeneity of 'Y. enterocolitica-like' species, which need to be addressed in the future. Also, newer techniques such as amplified fragment length polymorphism, VNTR-based typing and multilocus sequence typing should be applied to further understand epidemiology, population structure and evolutionary genetics of Y. enterocolitica and 'Y. enterocolitica-like' species.

Repetitive elements sequence (REP/ERIC)-PCR based genotyping of clinical and environmental strains of Yersinia enterocolitica biotype 1A reveal existence of limited number of clonal groups

REP- and ERIC-PCR genotyping were used to assess genetic heterogeneity among 81 strains of Yersinia enterocolitica biotype 1A isolated from India, Germany, France and the USA. Although both gave comparable results, ERIC fingerprints discriminated the strains better. The rep- (REP and ERIC) PCR genotyping showed that strains having different serotypes produced identical rep-profiles indicating their limited genetic diversity. The concatenated dendrogram of REP- and ERIC-PCR fingerprints clustered the biotype 1A strains into two major groups. In each group, majority of the Indian, European and American strains exhibited similarities ranging from 85% to >95%. Similarity of rep-PCR fingerprints amongst strains isolated from widely separated geographical regions revealed existence of a limited number of clonal groups of Y. enterocolitica biotype 1A. The present study failed to reveal unequivocal relationships between rep-PCR genotypes and the source of isolation. However, the clinical serotype O:6,30-6,31 strains formed a tight cluster and the aquatic O:6,30-6,31 strains formed a yet another tight cluster.

Characterization of the flexible genome complement of the commensal Escherichia coli strain A0 34/86 (O83 : K24 : H31)

Colonization by the commensal Escherichia coli strain A0 34/86 (O83 : K24 : H31) has proved to be safe and efficient in the prophylaxis and treatment of nosocomial infections and diarrhoea of preterm and newborn infants in Czech paediatric clinics over the past three decades. In searching for traits contributing to this beneficial effect related to the gut colonization capacity of the strain, the authors have analysed its genome by DNA-DNA hybridization to E. coli K-12 (MG1655) genomic DNA arrays and to 'Pathoarrays', as well as by multiplex PCR, bacterial artificial chromosome (BAC) library cloning and shotgun sequencing. Four hundred and ten E. coli K-12 ORFs were absent from A0 34/86, while 72 out of 456 genes associated with pathogenicity islands of E. coli and Shigella were also detected in E. coli A0 34/86. Furthermore, extraintestinal pathogenic E. coli-related genes involved in iron uptake and adhesion were detected by multiplex PCR, and genes encoding the HlyA and cytotoxic necrotizing factor toxins, together with 21 genes of the uropathogenic E. coli 536 pathogenicity island II, were identified by analysis of 2304 shotgun and 1344 BAC clone sequences of A0 34/86 DNA. Multiple sequence comparisons identified 31 kb of DNA specific for E. coli A0 34/86; some of the genes carried by this DNA may prove to be implicated in the colonization capacity of the strain, enabling it to outcompete pathogens. Among 100 examined BAC clones roughly covering the A0 34/86 genome, one reproducibly conferred on the laboratory strain DH10B an enhanced capacity to persist in the intestine of newborn piglets. Sequencing revealed that this BAC clone carried gene clusters encoding gluconate and mannonate metabolism, adhesion (fim), invasion (ibe) and restriction/modification functions. Hence, the genome of this clinically safe and highly efficient colonizer strain appears to harbour many 'virulence-associated' genes. These results highlight the thin line between bacterial 'virulence' and 'fitness' or 'colonization' factors, and question the definition of enterobacterial virulence factors.

Cloning, nucleotide sequencing, and functional analysis of a novel, mobile cluster of biodegradation genes from Pseudomonas aeruginosa strain JB2

We have identified in Pseudomonas aeruginosa strain JB2 a novel cluster of mobile genes encoding degradation of hydroxy- and halo-aromatic compounds. Nineteen open reading frames were located and, based on sequence similarities, were putatively identified as encoding a ring hydroxylating oxygenase (hybABCD), an ATP-binding cassette-type transporter, an extradiol ring-cleavage dioxygenase, transcriptional regulatory proteins, enzymes mediating chlorocatechol degradation, and transposition functions. Expression of hybABCD in Escherichia coli cells effected stoichiometric transformation of 2-hydroxybenzoate (salicylate) to 2,5-dihydroxybenzoate (gentisate). This activity was predicted from sequence similarity to functionally characterized genes, nagAaGHAb from Ralstonia sp. strain U2 (S. L. Fuenmayor, M. Wild, A. L. Boyes, and P. A. Williams, J. Bacteriol. 180:2522-2530, 1998), and is the second confirmed example of salicylate 5-hydroxylase activity effected by an oxygenase outside the flavoprotein group. Growth of strain JB2 or Pseudomonas huttiensis strain D1 (an organism that had acquired the 2-chlorobenzoate degradation phenotype from strain JB2) on benzoate yielded mutants that were unable to grow on salicylate or 2-chlorobenzoate and that had a deletion encompassing hybABCD and the region cloned downstream. The mutants' inability to grow on 2-chlorobenzoate suggested the loss of additional genes outside of, but contiguous with, the characterized region. Pulsed-field gel electrophoresis revealed a plasmid of >300 kb in strain D1, but no plasmids were detected in strain JB2. Hybridization analyses confirmed that the entire 26-kb region characterized here was acquired by strain D1 from strain JB2 and was located in the chromosome of both organisms. Further studies to delineate the element's boundaries and functional characteristics could provide new insights into the mechanisms underlying evolution of bacterial genomes in general and of catabolic pathways for anthropogenic pollutants in particular.

Silencing and reactivation of urease in Yersinia pestis is determined by one G residue at a specific position in the ureD gene

Yersinia pestis, the plague agent, is a naturally nonureolytic microorganism, while all other Yersinia species display a potent urease activity. In this report we demonstrate that Y. pestis harbors a complete urease locus composed of three structural (ureABC) and four accessory (ureEFGD) genes. Absence of ureolytic activity is due to the presence of one additional G residue in a poly(G) stretch, which introduces a premature stop codon in ureD. The presence of the same additional G in eight other Y. pestis isolates indicates that this mutation is species specific. Spontaneous excision of the extra G occurs at a frequency of 10(-4) to 10(-5) and restores a ureolytic phenotype to Y. pestis. The virulence of two independent ureolytic clones of Y. pestis injected either intravenously, subcutaneously, or intragastrically did not differ from that of the parental strain in the mouse infection model. Coinfection experiments with an equal number of ureolytic and nonureolytic bacteria did not evidence any difference in the ability of the two variants to multiply in vivo and to cause a lethal infection. Altogether our results demonstrate that variation of one extra G residue in ureD determines the ureolytic activity of Y. pestis but does not affect its virulence for mice or its ability to multiply and disseminate.

Yersiniae other than Y. enterocolitica, Y. pseudotuberculosis, and Y. pestis: the ignored species

The genus Yersinia is composed of 11 species, of which three (Y. pestis, Y. pseudotuberculosis, and Y. enterocolitica) have been exhaustively characterized. The remaining eight species (Y. frederiksenii, Y. intermedia, Y. kristensenii, Y. bercovieri, Y. mollaretii, Y. rohdei, Y. ruckeri, and Y. aldovae) have not been studied extensively and, because of the absence of classical Yersinia virulence markers, are generally considered to be nonpathogenic. However, recent data suggest that some of these eight species may cause disease by virtue of their having virulence factors distinct from those of Y. enterocolitica. These data raise intriguing questions about the mechanisms by which these species interact with their host cells and elicit human disease.

Efficient subtyping of Yersinia enterocolitica bioserotype 4/O:3 with pulsed-field gel electrophoresis

The purpose of this study was to evaluate the efficiency of pulsed-field gel electrophoresis (PFGE) for differentiation of isolates of Yersinia enterocolitica bioserotype 4/O:3 recovered from pig tongues at retail level in the Helsinki area during October and November of 1996. NotI generated 15 different PFGE patterns for 128 isolates. The discriminatory index did not exceed 74% due to the presence of two predominant PFGE-types, NA1 (58/128) and NB1 (25/128). After preliminary investigations with 35 enzymes, ApaI, XbaI, XhoI and SpeI were chosen for further characterization of the isolates. The discriminatory index increased from 74% to 93% and the number of different genotypes from 15 to 30 when isolates with the same PFGE pattern with NotI were further characterized with ApaI and XhoI, indicating that PFGE can be an efficient technique for characterization of bioserotype 4/O:3.

The 102-kilobase pgm locus of Yersinia pestis: sequence analysis and comparison of selected regions among different Yersinia pestis and Yersinia pseudotuberculosis strains

We report the complete 119,443-bp sequence of the pgm locus from Yersinia pestis and its flanking regions. Sequence analysis confirms that the 102-kb unstable pgm locus is composed of two distinct parts: the pigmentation segment and a high-pathogenicity island (HPI) which carries virulence genes involved in iron acquisition (yersiniabactin biosynthetic gene cluster). Within the HPI, three genes coding for proteins related to phage proteins were uncovered. They are located at both extremities indicating that the entire HPI was acquired en bloc by phage-mediated horizontal transfer. We identified, within the pigmentation segment, two novel loci that may be involved in virulence: a fimbriae gene cluster and a locus probably encoding a two component regulatory system similar to the BvgAS regulatory system of Bordetella pertussis. Three genes containing frameshift mutations and two genes interrupted by insertion element insertion were found within this region. To investigate diversity among different Y. pestis and Yersinia pseudotuberculosis strains, the sequence of selected regions of the pgm locus and flanking regions were compared from 20 different Y. pestis and 10 Y. pseudotuberculosis strains. The results showed that the genes interrupted in Y. pestis are intact in Y. pseudotuberculosis. However, one of these mutations, in the bvgS homologue, is only present in Y. pestis strains of biovar Orientalis and not in those of the biovars Antiqua and Medievalis. The results obtained by analysis of variable positions in the sequence are in accordance with historical records, confirming that biovar Orientalis is the most recent lineage. Furthermore, sequence comparisons among 29 Yersinia strains suggest that Y. pestis is a recently emerged pathogen that is probably entering the initial phase of reductive evolution.

Presence of Yersinia enterocolitica in tissues of orally-inoculated pigs and the tonsils and feces of pigs at slaughter

In order to study the early events associated with infection of swine by Yersinia enterocolitica, 42 five-week-old crossbred piglets were inoculated per os with approximately 10(8) Y. enterocolitica O:3. Groups of 5 animals (and one negative control) were euthanized 30 min, 3, 6, 12, 24, 48 and 72 h following the infection. Palatine tonsils, retropharyngeal and mesenteric lymph nodes, esophagus, duodenum, jejunum, ileum (and Peyer's patches), stomach, liver, spleen and feces (from colon) were collected and analyzed for the presence of Y. enterocolitica by standard bacteriological procedures. Natural infections were also analyzed, as a complementary study, by taking one-gram samples of fecal material and tonsils from 291 pig carcasses less than 3 h after slaughter and culturing them for Y. enterocolitica using a cold enrichment technique. Within 30 min, Yersinia enterocolitica O:3 was already present at most sites. The presence of Y. enterocolitica in the liver of 3 out of 10 animals and also in the spleen of 3 out of 10 piglets, within the first 3 h postinfection, but not at later times (with one exception), probably indicated a transient bacteremia accompanying the initial stages of infection. The tonsils were colonized in most animals (13/20) as the bacteria remained present from 12 to 72 h postinfection, while only 4 out of 20 fecal samples were found to be positive over the same period. Up to 10(4) colony-forming units of Y. enterocolitica per gram of tonsil and fecal material were recovered. Finally, among the 291 animals sampled at the abattoir, a total of 79 were found positive, 70 of the tonsils sampled were positive, and bacteria were recovered in 17 fecal samples. It is therefore suggested that palatine tonsils are the most reliable tissue for the indication of an infection/colonization by Y. enterocolitica O:3 in swine and that the removal of this tissue during the slaughter process should be considered in order to minimize the possibility of contamination of meat products.

Evidence that mortality from Vibrio vulnificus infection results from single strains among heterogeneous populations in shellfish

Vibrio vulnificus is the leading cause of food-related mortality reported in the state of Florida. It is normal microflora in marine environments, where seawater and molluscan shellfish are the primary vectors of V. vulnificus disease. Risk correlates with seasonally high numbers of V. vulnificus bacteria during the summer months. Currently, the infectious dose for humans, as well as whether the disease is caused by single or multiple strains found in molluscan shellfish, is unknown. In this work, we studied pulsed-field gel electrophoresis profiles of V. vulnificus strains isolated from blood and oysters associated with V. vulnificus disease. Results showed that ca. 10(3) V. vulnificus bacteria/gram of oyster and higher concentrations were associated with human infections and that a single V. vulnificus strain, evidenced by pulsed-field gel electrophoresis profiles, was isolated from human tissues.

Genomic analyses of Salmonella enteritidis phage type 4 strains from Austria and phage type 8 strains from the United States

Forty illness associated phage-type (PT) 4 and PT 8 strains of Salmonella enteritidis were analyzed by the pulsed-field technique of clamped homogeneous electric fields (CHEF) electrophoresis. Using NotI and XbaI, the 40 strains were subdivided by each enzyme into seven restriction endonuclease digestion profiles (REDP). The 35 PT 4 isolates from Austria were subdivided into six NotI and five XbaI REDP, while the five PT 8 isolates from the United States displayed a single NotI and two XbaI REDP. When highly-concentrated, uncleaved genomic DNA was subjected to CHEF electrophoresis, plasmid DNA in the size range of 350 kb relative to a linear DNA standard was discernible in 38 of the 40 strains. Subsequent isolation and restriction analyses of plasmid DNA from one strain (E40) revealed a single plasmid (pE40; ca. 54 kb) with one XbaI and two NotI cleavage sites that was similar in size to the S. enteritidis virulence plasmid pRQ29. Hybridization of the PE40 probe with S. enteritidis genomic DNAs identified a 54 kb fragment within the XbaI REDP and two fragments, 20 and 34 kb, in NotI REDP of plasmid-positive strains. It was not possible to identify plasmid-specific bands in NotI REDP without hybridization due to comigrating chromosomal and plasmid DNA fragments. Regardless of PT, all 40 S. enteritidis strains showed highly related REDP. The similarity between PT 4 and PT 8 strains as further revealed by Dice similarity coefficients was 90% to 95% for NotI REDP and 79% to 93% for XbaI REDP. These results support the hypothesis that the pandemic observed today is the result of the efficient spread of a single clone, or clusters of closely related clones, of S. enteritidis.

Discriminatory power and application of ribotyping of Yersinia enterocolitica O:3 in an epidemiological study

Ribotyping performed with five restriction endonucleases was used in an attempt to subtype Yersinia enterocolitica serotype O:3 and also as a tool for clonal analysis. DNA from organisms under study (48 isolates from diarrheic human feces, 24 from food, and 5 reference strains) was tested by Southern hybridization using a DNA probe carrying an rRNA operon from Escherichia coli. Strains were grouped into seven ribotypes by the HindIII restriction endonuclease, into five ribotypes by Ncil, Bg/l, and Sa/l; and into two ribotypes by EcoRI, resulting in a discrimination index (DI) of 0.37, 0.17, 0.43, 0.13, and 0.03 for the five endonucleases. By combining the results obtained with two or more restriction endonucleases, a further discrimination was registered, the most efficient combination (in terms of discriminatory power vs. cost in work, time, and money) for routine typing being HindIII-Bg/l (9 types, DI=0.58). In the clonal analysis, results obtained with the five restriction endonucleases allowed us to define 11 groupings or clonal lines, which showed a remarkable degree of genetic heterogeneity (genetic distance coefficients between 0.03 and 0.73) and were grouped into two major clusters. One cluster included 93% of the strains and eight lines. At least two of the most frequent lines can be considered endemic in Asturias, Spain, because organisms belonging to these lines have been circulating and causing human yersiniosis in recent years and have also been isolated from commercial raw meat products. Two Ncil ribotypes from the series under study (92.2% of strains included in the prevalent cluster) were similar but not identical to ribotypes of 0.3 organisms from other geographic areas described in the literature, indicating that the genetic structure of prevalent human pathogens of this serotype is basically clonal.

Detection of pathogenic Yersinia enterocolitica in environmental waters by PCR

The isolation of pathogenic strains of Yersinia enterocolitica from food and water samples by culture is time-consuming and unreliable. A two-step PCR procedure has been developed which, after a period of bacterial enrichment, can detect and confirm the presence of pathogenic Y. enterocolitica within a single day. This PCR method works effectively for a range of environmental water types, including reticulated waters, reservoirs and creeks. A survey of environmental waters in Victoria, Australia, showed that the PCR method detected pathogenic Y. enterocolitica in water sampled from four separate sites (two creeks and two reservoirs). Repeat samplings of the two reservoirs yielded PCR-positive results on all but one occasion. Culture analysis of the same samples detected pathogenic Y. enterocolitica in only one sample, indicating that the PCR can detect pathogenic Y. enterocolitica which are undetectable by culture. Results from this study confirm that potentially pathogenic strains of Y. enterocolitica can exist in environmental waters.

Potential sources of sporadic human infection with Yersinia enterocolitica serovar O:8 in Aomori Prefecture, Japan

In November 1992 and June and August 1993 rectal contents from 204 small mammals living in the wild were collected and examined for the presence of Yersinia enterocolitica serovar O:8 to clarify the source of human infections caused by this microbe in the Tsugaru Region of Aomori Prefecture, Japan. Serovar O:8 was isolated from 10 (5.2%) of 193 wild rodents trapped in June 1993 (9 of 107) and August 1993 (1 of 23) but not from animals trapped in November 1992 (0 of 63). This serovar was not isolated from 11 moles. From May to September 1993, 12 human patients were found to have become ill and to be infected with Y. enterocolitica O:8. The patients lived in the same districts where the wild rodents harboring serovar O:8 were trapped. Two different patterns by restriction enzyme analysis of the virulence plasmid were observed. One pattern obtained by restriction enzyme analysis of the virulence plasmid was observed in 20 isolates from 11 human patients and 9 wild rodents, and the other was observed in 2 isolates from 1 human patient and 1 wild rodent. These findings indicate that wild rodents seem to play an important role as a source of human Y. enterocolitica O:8 infection.