Development and testing of a synthetic oligonucleotide probe for the detection of pathogenic Yersinia strains

Yersinia enterocolitica: Epidemiological Studies and Outbreaks

Yersinia enterocolitica is the most common bacteriological cause of gastrointestinal disease in many developed and developing countries. Although contaminated food is the main source of human infection due to Y. enterocolitica, animal reservoir and contaminated environment are also considered as other possible infection sources for human in epidemiological studies. Molecular based epidemiological studies are found to be more efficient in investigating the occurrence of human pathogenic Y. enterocolitica in natural samples, in addition to conventional culture based studies.

Low occurrence of pathogenic Yersinia enterocolitica in clinical, food, and environmental samples: a methodological problem

While Yersinia enterocolitica is an important pathogen, which can cause yersiniosis in humans and animals, its epidemiology remains obscure. The pig is the major reservoir of pathogenic Y. enterocolitica of bioserotype 4/O:3, the most common type found in humans. Y. enterocolitica is thought to be a significant food-borne pathogen, although pathogenic isolates have seldom been recovered from foods. The low isolation rate of this pathogenic bacterium in natural samples, including clinical, food, and environmental samples, may be due to the limited sensitivity of culture methods. During the last decade, numerous DNA-based methods, such as PCR and colony hybridization assays, have been designed to detect pathogenic Y. enterocolitica in natural samples more rapidly and with better sensitivity than can be achieved by culture methods. In addition, the occurrence of pathogenic Y. enterocolitica in natural samples is clearly higher with PCR than with culture methods. The methods available for detection of pathogenic Y. enterocolitica in natural samples are reviewed in this article.

Probes and polymerase chain reaction for detection of food-borne bacterial pathogens

DNA-hybridization and the polymerase chain reaction (PCR) are techniques commonly used to detect pathogenic bacteria. In this paper, the use of these techniques for detection of Salmonella, E. coli, V. cholerae, non-O1 Vibrio, Yersinia enterocolitica, Campylobacter, Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, Clostridium perfringens, and C. botulinum is reviewed with emphasis on application in food microbiology. In food control, DNA-techniques have most often been used in a 'culture confirmation' fashion, i.e. bacteria are enriched and sometimes even purified by traditional culture procedures and thereafter identified by the use of DNA-based methods. The most desirable approach is, however, to detect organisms directly in the food, but major problems remain to be solved before this can be routinely performed.

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

Sixty strains of Yersinia enterocolitica from five serogroups (O:3; O:9; O:8; O:5; and O:5,27) and eight non-Y. enterocolitica strains, recovered from diverse sources (humans, animals, food, and the environment) in Europe, Argentina, and the United States, were examined by the pulsed-field gel electrophoresis (PFGE) technique of contour clamped homogeneous electric field electrophoresis (CHEF) by using NotI and XbaI as restriction enzymes. NotI and XbaI generated 36 and 33 restriction endonuclease digestion profiles (REDP), respectively. By combining the results of both enzymes, 42 unique genomic groups were differentiated. DNA fragments were transferred to nylon membranes and hybridized with digoxigenin-labelled oligonucleotide probes to the ail gene and virulence plasmid to determine hybridization patterns and the potential virulence of the strains. The strains were tested for the presence of the plasmid by PFGE-CHEF and phenotypic characteristics encoded for by the virulence plasmid. Thirty of the 60 Y. enterocolitica strains tested harbored the virulence plasmid. The specificity of the ail and pYV probes was 100% when tested with 68 Yersinia strains and 19 different non-Yersinia strains. Sixteen selected Y. enterocolitica strains were tested for their virulence by lethality in iron- and desferrioxamine-sensitized mice. No correlation between REDP and the virulence of the strains was observed. The observed REDP and the hybridization patterns were very homogeneous within a serogroup and independent of the source of isolation. In addition, PFGE-CHEF was shown to be valuable in identifying and confirming serogroups. Principal component analysis of Dice similarity indices from REDP was an excellent tool for determining genetic relatedness among strains.

Digoxigenin-labelled inv- and ail-probes for the detection and identification of pathogenic Yersinia enterocolitica in clinical specimens and naturally contaminated pig samples

A non-radioactive colony hybridization method was developed for the rapid detection of Yersinia enterocolitica in primary isolates and for differentiation between pathogenic and non-pathogenic strains. The method is based on, respectively, the presence of the inv-locus in all Yersinia spp. and the presence of the ail-gene in pathogenic Y. enterocolitica only. Hybridization results with ail-probes of 132 strains of Y. enterocolitica were in good agreement with pathogenicity phenotypes as indicated by a tissue culture invasion (TCI) assay and by serotyping. All TCI+ strains and only two TCI- strains were positive by hybridization with ail. Hybridization results with inv- or ail-probes of 150 primary isolates of human, animal or slaughterhouse origin were compared with those of conventional methods to detect and identify Y. enterocolitica. All samples that were positive for Yersinia spp. by cultivation (four of 66) or were positive for pathogenic Y. enterocolitica by cultivation and serotyping (six of 84) were also positive by hybridization with, respectively, the inv- or ail-probe. In three slaughterhouse swab samples, in which Yersinia spp. were not detected by cultivation (2%), strong positive hybridization signals were obtained with the inv- and/or ail-probe. Four other swab samples which were negative by cultivation produced weak positive signals by hybridization with inv- and/or ail-probes. These results indicate that the method can be used for (1) the identification of pathogenic Y. enterocolitica isolates and (2) the detection of Yersinia spp. in primary isolates of naturally contaminated samples.

Molecular methods for environmental monitoring and containment of genetically engineered microorganisms

Plans to introduce genetically engineered microorganisms into the environment has led to concerns over safety and has raised questions about how to detect and to contain such microorganisms. Specific gene sequences, such as lacZ, have been inserted into genetically engineered microorganisms to permit their phenotypic detection. Molecular methods have been developed based upon recovery of DNA from environmental samples and gene probe hybridization to specific diagnostic gene sequences for the specific detection of genetically engineered microorganisms. DNA amplification using the polymerase chain reaction has been applied to enhance detection sensitivity so that single gene targets can be detected. Detection of messenger RNA has permitted the monitoring of gene expression in the environment. The use of reporter genes, such as the lux gene for bioluminescence, likewise has permitted the observation of gene expression. Conditional lethal constructs have been developed as models for containment of genetically engineered microorganisms. Suicide vectors, based upon the hok gene have been developed as model containment systems.

Convenient agarose medium for simultaneous determination of the low-calcium response and Congo red binding by virulent strains of Yersinia enterocolitica

A simple, efficient method for identification and differentiation of Yersinia enterocolitica containing virulent plasmid-bearing clones is described. The method is based on temperature of incubation and the low calcium response of the organism in an agarose Congo red medium.

Comparative study of a DNA hybridization method and two isolation procedures for detection of Yersinia enterocolitica O:3 in naturally contaminated pork products

We compared a DNA-DNA hybridization assay, using a synthetically produced oligonucleotide probe, and two conventional isolation procedures (methods A and B) with regard to their relative efficiency in detecting Yersinia enterocolitica O:3 in naturally contaminated pork products. Method A was as described by Wauters et al. (Appl. Environ. Microbiol. 54:851-854, 1988). Method B has been recommended by the Nordic Committee on Food Analysis (method no. 117, 1987). The genetic probe was used in a colony hybridization assay to detect virulent yersiniae at each of the isolation steps with composed methods A and B. A total of 50 samples of raw pork products obtained from 13 meat-processing factories in Norway were examined. Y. enterocolitica serogroup O:3, biovar 4, was isolated from altogether 9 (18.0%) of the samples by using the two isolation procedures. In contrast, colony hybridization using the genetic probe indicated that 30 (60.0%) of the samples contained virulent yersiniae. All samples which were positive on cultivation were also positive by hybridization. The results indicate that the occurrence of pathogenic Y. enterocolitica in Norwegian pork products is substantially higher than previously demonstrated and, therefore, reinforce our suggestion that pork products represent an important potential source of human infection in Norway. The results also indicate that the use of conventional isolation procedures may lead to considerable underestimation of pathogenic Y. enterocolitica in pork products.

Identification of a conjunctivitis-associated gene locus from the virulence plasmid of Yersinia enterocolitica

The virulence plasmid (pYV) of Yersinia enterocolitica is necessary for production of conjunctivitis in guinea pigs and for mouse lethality. To identify the genes responsible for production of conjunctivitis in guinea pigs, we subcloned the BamHI and SalI restriction fragments of the virulence plasmid of Y. enterocolitica A2635 (serotype O:8) into derivatives of the broad-host-range plasmid pRK290 and introduced the constructions into plasmid-negative Y. enterocolitica strains. A mild, transient conjunctivitis was evident 24 h after inoculation with strains containing a 2.8-kilobase (kb) BamHI fragment of pYV. These strains were cytotoxic to HEp-2 cells but did not cause death in iron-loaded adult mice. When the 2.8- and adjacent 0.5-kb BamHI fragments were deleted from the virulence plasmid of a fully virulent Y. enterocolitica isolate, the resultant strain did not cause conjunctivitis in guinea pigs and was not cytotoxic to HEp-2 cells. However, the strain with the deletion appeared to be more virulent for mice, with more rapid dissemination after orogastric inoculation, compared with that of the parent strain. When the deletion was complemented by introduction of a plasmid containing the 2.8-kb BamHI fragment, the strain again caused conjunctivitis but had decreased virulence for mice.

A synthetic oligonucleotide probe and a cloned polynucleotide probe based on the yopA gene for detection and enumeration of virulent Yersinia enterocolitica

We compared a synthetically produced 19-mer oligonucleotide probe with a polynucleotide probe consisting of a cloned fragment of the virulence gene yopA for their relative efficiencies in identification and enumeration of virulent Yersinia enterocolitica. The probes were used in DNA-DNA colony hybridization assays to differentiate 70 Yersinia strains with known plasmid profiles. All 19 strains harboring the 40- to 50-megadalton virulence plasmid were positive in the hybridization assay, whereas their isogenic derivatives lacking this plasmid were negative. Both probes correctly identified plasmid-bearing variants of Y. enterocolitica serogroups O:3, O:5,27, O:8, O:9, O:13, and O:21 from three continents. In contrast, none of the probes hybridized with DNA from 32 environmental yersiniae belonging to 26 serogroups not associated with disease. Colony hybridization was used to detect and enumerate virulent Y. enterocolitica in three artificially contaminated food samples. Despite a large background of indigenous bacteria (3 x 10(4) CFU), the efficiency of enumeration ranged from 33 to 82%. The use of nylon filters did not impair the growth of virulent yersiniae. Both probes showed a perfect concordance in their specific differentiation and enumeration of virulent Y. enterocolitica. DNA colony hybridization with these two probes permitted rapid and reliable identification of all common pathogenic serogroups without the need for enrichment or esoteric identification protocols.