|
McCall Cameron Akin lost her life last week to an E. coli infection. And parents around the Atlanta area are trying to figure if their children came into contact with this potentially deadly bacteria that surfaced earlier this summer at White Water Park.
E. coli, formally known as Escherichia coli, is the name of a species of bacteria, and within this species are many different strains of E. coli. Strains of a bacterial species can be thought of in the same way as breeds of dogs; dogs are all one species, canine, but there are many different breeds and some breeds are more closely related than others. The strains of E. coli are as different and as varied as dogs; some strains of E. coli are found in the intestines of healthy humans and are beneficial, other strains cause diarrhea, and still other strains that are potentially deadly, just to name a few.
The strain of E. coli that was seen earlier this summer at White Water Park was E. coli O157:H7. This strain of E. coli is one of the only two members of the enterohemorragic category of diarrhea causing E. coli. Researchers at Emory University are currently investigating another diarrhea causing E. coli, but it is in the enterotoxigenic category.
Enterotoxigenic E. coli, ETEC, are not a health threat to adults or children in the greater Atlanta area. This is due to the water treatment plants that treat the water in such a way that these bacteria are usually killed, making the water that goes to homes and businesses safe to drink. But in other countries where water treatment does not meet US standards, or is not present at all, ETEC, pose a serious threat to young children and travelers.
In less-developed countries, the average child has up to one ETEC infection a year during the first three years of life. An ETEC infection causes diarrhea which can lead to dehydration. Due to the decreased number of hospitals and the lack of basic medical supplies in less-developed countries, becoming dehydrated is a much more serious condition than here in the US.
Travelers to less-developed countires are also at risk for ETEC infections. Travelers' diarrhea is often caused by ETEC present in the water supply in foreign countries. Travelers can come in contact with ETEC through simply drinking the water from the local water supply or by eating fruits and vegetables that have been grown in local water. Although most people who contract travelers’ diarrhea due to an ETEC infection recover within a few days, these few days are never the highlight of a vacation. Also, although rare a few outbreaks of ETEC diarrhea in the United States and other developed countries have been reported.
No matter the person’s age or how the ETEC got inside the body, the same thing happens once they are present. ETEC attach to the small intestine via protein structures that extend from the cell wall, pili, and produce toxins. These toxins induce water to leave the cells lining the small intestine. Then this water is excreted from the body along with the contents of the small intestine as diarrhea.
Since ETEC must adhere to the intestine before they can produce these toxins, the synthesis of pili by ETEC is important to understand in an effort to reduce the number of cases of diarrhea due to ETEC. Additionally, pili protein-based vaccines have been successful in preventing ETEC diseases in animals and it is possible that this type of vaccine would protect humans from ETEC diseases.
Dr. June Scott is the head of a group of scientists at Emory University trying to figure out just how the pili of ETEC are produced. Although there are three different types of pili, they have found that the production of any type of pili requires four linked genes, the coo genes. The rate at which these genes are expressed as the proteins they code for is controlled by at least three specific sections of DNA located close to the genes, called promoters, and a protein named Rns. These promoters and Rns individually and jointly control the expression of these genes by allowing or not allowing enzymes and other proteins to bind at certain sites in the coo genes.
Additionally, there is another region of DNA located further away from the coo genes called urr. This section of DNA also affects the rate at which the coo genes are used to make pili. When urr is present, the coo genes are expressed as pili at a rate approximately ten times greater. It is not currently known how this piece of DNA acts, but it is thought that since urr is so far away from the coo genes that this region would have the same effect even if it was on a different piece of DNA. A region of DNA that has this ability said to act in trans. Sara Fitzgerald, who entered Dr. Scott's lab through the Summer Undergraduate Research Experience organized through the Hughes Science Initiatives Office, has spent 10 weeks this summer determining if in fact urr does act in trans. Surprisingly, Fitzgerald has found that urr does not act in trans, and therefore must be on the same piece of DNA to have an effect on the coo genes.
Although this finding is only a small step in determining how pili are produced, huge scientific discoveries are made through a series of small steps. A vaccine that would allow travelers to drink water wherever they are, and rid children all over the world of an infection they each get up to three times in their first three years of life, would be a huge scientific discovery that was the result of many small steps.
|
