Higher order taxa
Bacteria; Proteobacteria; Gammaproteobacteria; Enterobacteriales;Enterobacteriaceae
Y. enterocolitica, Y. pestis, Y. pseudotuberculosis
Description and significance
Y. enterocolitica are gram-negative, rod-shaped bacteria that give rise to food poisoning. Other species in this family include Y. pseudotuberculosis and Y. pestis, both of which are known pathogens. Y. enterocolitica are found most often in feces and wounds, but they can also contaminate food and water sources. However, only a few strains of Y. enterocolitica cause diseases in human and especially in pigs . Understanding Y. enterocolitica is important due to increasing numbers of infections by this species in the past 30 years. This pathogen can induce gastroenteritis, which produces gastrointestinal mucous membrane inflammation similar to that caused by salmonella species .
Isolation of Y enterocolitica enhances the understanding of this organism as pathogen. A few techniques were used to isolate Y. enterocolitica. A “cold-temperature enrichment” procedure was performed from stool samples in 1975 at University of California, Los Angeles. Cold enrichment method takes into account the slow growth of this organism at 37 C by treating the sample with saline and storing at 4 C before proceeding to the normal examination and culturing of Y. enterocolitica. This has enhanced the recovery of Y. enterocolitica compared to the conventional procedure without cold enrichment . In addition, MacConkey agar and medium that contains Trypticase soy broth, yeast extract, bile salts and Irgasan at 12 C can also recover certain strains of Y. enterocolitica. These methods were useful in isolating virulent strains from procine tongues .
Y. enterocolitica strain 8081 has a circular DNA chromosome of 4,615,899 bp. The number of coding sequences (CDSs) is 4037 with 7 rRNA operons and 81 tRNA. The GC content of the chromosome is 47.27%. Average gene size is 968 bp. The chromosome also contains 60 IS elements and 4 prophage regions. In addition to the chromosome, Y. enterocolitica has four plasmids. pYVe8081 is 67,721nt in length , p29807 is 2682 nt , pYVa127/90 is 66591nt long and pYVe227 is 69673 nt . In terms of pathogenicity, Y. enterocolitica needs both chromosome and plasmid to work as a pathogen, because both the chromosome and the pYV pathogenic plasmid contains gene necessary for virulence  . Also, the virulent strains contain plasmids that encodes genes for “low-Ca21 response”, which give rise to pathogenic properties .
The unique features that distinguish the Y. enterocolitica genome from all other Yersinia species are the coenzyme B12 biosynthetic (cbi) and 1,2-propanediol-degradation (pdu). These genes clusters are located on a genomic island that is about 40kb in size. Coenzyme B12 is needed to breakdown 1,2-propanediol for carbon and energy utilization, and it is produced only when no oxygen is present in the environment. It has been suggested that the pdu operon is the locus for lateral gene transfer in both Salmonella and E. coli divergence .
Cell structure and metabolism
Y. enterocolitica are able to swim at 25 C but lose mobility at 37C. They are an anaerobe that uses glucose as energy source through fermentation. Most strains also reduce nitrates. However, when they are artificially cultured in lab settings, lactose fermentation is inhibited by the addition of bile salts in some media. When cultured in “triple sugar iron medium”, Y. enterocolitica are able to produce urease, but lose their ability to produce hydrogen sulfide . In addition, Y. enterocolitica in anaerobic conditions also uses coenzyme B12 to degrade 1,2-propanediol and use it as carbon and energy sources .
Glucose fermentation: C6H12O6 → 2C2H5OH + 2CO2 + 2 ATP
Y. enterocolitica are able to use iron as growth factor without producing a chelater that is usually necessary for the process. Most prokaryotic organisms uptake iron through an iron chelater called siderophore. Y. enterocolitica, however, uses siderophores from other bacteria for its own iron intake process. For example, it uses deferoxamine that is produced from Streptomyces pilosus. Research has found that pathogenicity is positively correlated to iron usage. Different needs for iron also potentially explains why different strains of Y. enterocolitica vary in their degree of virulence.
Ecology & Pathology
Y. enterocolitica are pathogens that invade eukaryotic organisms often through the means of food-intake . Virulent strain 0:8 is most common in the United States. Research revealed that this infection has 2.8% prevalence . However, patients that potentially harbor the bacteria with no pathogenic symptoms were not taken into account. Since this organism proliferates better in cold environments, most virulent strains are found in Canada and Europe with strains 0:3 and 0:9 as the most common serotypes. The infection does not show predominance in particular racial groups or gender groups. However, children are reported more likely to be infected while the elderly patients are more likely to develop arthritis. A sample collection from 1988 through 1991 has shown that 77.6% infections occur in children 12 months old or younger, making Y. enterocolitica the second most common cause of bacterial gastric infection in children .
Diarrhea is the most common symptoms among those infected. It may be accompanied by stomach ache for 1-3 weeks and a mild degree of fever. Some patients may have bloody feces, and around 40% vomit. In more severe cases, patients may develop mesenteric adenitis, mesenteric ileitis, or acute pseudoappendicitis. Such patients may experience increase leukocyte production and nausea. Ulcer of the mouth and potential need for appendectomy (removal of appendice) are also possible. Approximately 2% of patients report the development of arthritis after infection with Y. enterocolitica. Such symptoms usually appear 1-2 weeks after gastrointestinal infection, and can last up to 4 months. In addition, patients that have alcoholism, diabetes or immune system defects are more likely to develop septicemia, a type of blood poisoning. The mortality rate is low for normal infections, but increases to 34-50% if bacteremia, a condition of bacteria in blood, is present .
Infection with Y. enterocolitica can be directly from contaminated food, water, pork and tofu, or transmitted from pets such as dogs, cats and swine. There is no evidence for insect or interpersonal transmission. Also, people who over ingest iron or those who use drugs that contain deferoxamine are high risk groups for Y. enterocolitica infection since iron is an important nutrient for the virulent strains of bacteria. The bacteria invade the hosts by destroying the host tissues. This process can be done by two mechanisms, one mediated by the chromosome, the other by the plasmid. Chromosomal action includes secretion of enterotoxin that induces diarrhea or vomiting. Plasmid action depends on antigen and calcium responses of the host cell membrane that allows the bacteria to bind to the host cell . The bacterial genome contains a gene called the inv gene, which produces proteins that signal the invasion of epithelial cells in ileum. This in turn leads to destruction of mucosal layers.
Application to Biotechnology
Under low calcium ion conditions, Y. enterocolitic secrets a group of proteins call Yops, which are plasmid encoded. The secretion of these proteins is not triggered by recognition or signal sequences. Comparison between the secretion of YopH, YopE and YopQ has shown that there is no sequence similarity between the regions that encode these proteins, so the release of Yops is independent of sequence, but dependent on conformational change in the absence of calcium ions. Researchers observe that YopH is able to fuse with the a-peptide of 13-galactosidase with and without alkaline phosphatase to produce a hybrid protein. This suggests that Yops secreted by Y. enterocolitica may be used to carry non-self antigens and to produce “chimeric-proteins” .
In addition, Y. enterocolitica is able to produce a unique periplasmic binding protein that takes up polygalacturonic acid with pectin. X-ray crystallography revealed structural similarity between the binding protein and galactose-specific CBMs. Researchers suggest that Y. enterocolitica may have a special role in transport of polygalacturonic acid .
The Department of Immunology at National University of Córdoba, Argentina, is conducting research to determine the effect of IL-12p40 on reactive arthritis (ReA), a chronic symptom after infection with Y. enterocolitica. IL-12 is a cytokine that comes with two subunits, p40 being one of the subunits. It was observed that mice with IL-12p40 deficiency demonstrate greater chance of defective immune systems. This research studies the involvement of antigens and Toll-like receptor (TLR) expression in causing ReA. TLR binds to portions of bacteria that give rise to arthritis. Understanding the mechanism of ReA development may enable the formulation of treatment for this condition. In order to study for this, wild-type and IL-12p40 deficient mice were infected with Y. enterocolitica. Subsequently, bacterial colonies were analyzed by Peyer’s patches and ELISA. It was found that bacterial recovery was much higher in IL-12p40 deficient mice; a increase in mRNA for TLR was also observed. A conclusion has been made that the absence of IL-12p40 contributes to ReA due to inability to remove Y. enterocolitica effectively. The incomplete removal of bacteria consequently triggers TLR expression, which leads to articular inflammatory response .
Another study attempts to clarify the relationship between the presence of food and the production of N-acyl-1-homoserine lactones (AHLs), a quorum-sensing signal molecule, by Y. enterocolitica. In order to trace the production of this molecule, a fluorescent assay examined colonies in lab-induced environments and in various food sources. It was found through thin layer chromatography that AHLs are preferentially produced in fish and meat while inhibited in vegetables. This research suggests that quorum sensing mechanism is important to Y. enterocolitica to intake nutrients and to reside in specific environments. However, the physiological significance of AHL production still remains unknown .
The research conducted by Riber and Jungersen addresses the issue in National Brucella surveillance program. The conventional system, due to extremely similar LPS o-antigens, had difficulty discriminating between infections with Y. enterocolitica and that with Brucella. Therefore, this study attempts to develop surveillance methods that provide greater differential ability. Since LPS antigens are highly similar, non-LPS Brucella antigens were used to develop new testing techniques. In a field study, 200 pigs were artificially infected with Y. enterocolitica and screened with high interferon-gamma (IFN-gamma) assay and skin test to see if the screening would give any false-positive results when there is no Brucella infection. On second tests, the result showed that with conventional surveillance method, 36 out of 200 pigs gave false positive results while IFN-gamma assay and skin test correctly indicate that there none were infected with Brucella. In short, the research suggested that IFN-gamma assay and skin test with non-LPS antigens are more powerful screening tests to discriminate between Brucella and Y. enterocolitic infections .
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Edited by Angela Chen, student of Rachel Larsen and Kit Pogliano