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| Biotech Updates |
| Genome of O157:H7 Strain of E. coli Gives Insights Into the Genetics of Food-borne Disease - January 26, 2001 |
| On January 25, 2001, University of Wisconsin-Madison researchers published
a completed sequence of all the DNA that encodes all the genes of the deadly
food-borne O157:H7 strain of the E. coli bacterium.
While O157:H7 has been found in many foods, including vegetables and fruit juices, it is most infamous as a strain that contaminates hamburger, gaining national attention in the Jack-in-the-Box outbreak in the mid 1990's in the state of Washington. According to a UW-Madison press release, there are currently no effective treatments for E. coli O157:H7, which causes a severe form of bloody diarrhea and can also release toxins that damage kidneys and cause renal failure. E. coli is found in the intestines of animals, including humans, and also exists in fields and streams. The O157:H7 strain, while rare, is probably the most dangerous to humans. The strain is a cousin of the harmless K12 strain of E. coli that the Wisconsin researchers had sequenced in 1997. The K12 strain has slightly over 4000 genes. Of these, about genes are also found in O157:H7, and around 500 genes are found only in K12 and not in 0157:H7. In sequencing O157:H7, the researchers found about 1,300 new genes not found in K12.The genes unique to O157:H7 are of particular interest because among these are likely to be the genes that enable the strain to harm humans. These genes, and the proteins they encode, are also good targets for diagnostic kits to specifically detect the deadly strain, for potential vaccines to increase a person's resistance to it, and for treatments to reduce the harm of established infections.The sequencing is an important step in the science of genomics, the part of genetics that tries to figure out the sequences, locations, functions and interactions of all the genes in an organism. Now researchers have three key, complete DNA sequences: the harmless K12, the deadly O157:H7, and the human (finished in summer 2000). Probing the genomes of E. coli and humans will likely give new insights into how bacteria cause disease and how the human body fights it.Researchers can now explore questions about which genes can make a bacterium harmful, which ones can make a harmful bacterium harmless, and how the genes of the infecting bacterium interact with the genes of the human. Mapping the genes and analyzing their arrangement have given new insights into how genes change and move across a bacterial population. The researchers concluded that the O157:H7 strain has picked up or exchanged large clusters of genes. Some of the clusters can be described as "islands of pathogenicity" within a stream of genes not involved in infection.The researchers suspect that different strains and even different species of bacteria can shuffle within an individual bacterium and shuttle these genes back and forth between different strains or populations. A likely shuttle is bacterial viruses that can move large chunks of DNA that can then be inserted into the main loop of DNA that makes up the single 'chromosome' of most bacteria.The researchers suggest that bacteria from different groups, such Salmonella, Shigella, and Yersinia, can relatively easily harbor and exchange genes. If so, then the "pathosphere", or the collection of all genes available to a bacterium for causing disease, is not limited to its near cousins, but to genes that reside in far-more-distant relatives.How scientists view the ebb and flow of genes, especially disease-inducing genes, can affect how public health officials assess issues such as the generation and spread of strains of bacteria resistant to antibiotics. Links: UW-Madison news release: http://www.news.wisc.edu/releases/view.html?id=5722 Nature, the scientific journal: http://www.nature.com/nature/links/010125/010125-4.html And http://www.nature.com/nsu/010125/010125-9.html A general site on genomics: www.sciencegenomics.org |
| For more information, contact:
Tom Zinnen 425 Henry Mall Madison WI 53706 608-265-2420 zinnen@biotech.wisc.edu |
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