Saturday, December 15, 2007

Microbial War


First it was hamburger, then municipal water, apple cider, swimming in the lake, the day-care center, the petting zoo ...... and now, spinach. Humans have been contracting foodborne infectious diseases in many environments and products. For example, last year the toxin, known as Shiga toxin- producing Escherichia coli was found in bagged spinach that implicated the illnesses of mild intestinal disease to severe kidney complications to over one hundred people, mostly affecting children under the age of eighteen.


“If you survived the Shiga toxin and the after-effects of food poisoning you may have been the innocent victim of a battle for survival between predator and prey.”


The bacterial ciliated protozoan Tetrahymena (shown left in picture) is fifty times the size of its bacteriophage (bacteria that carry a virus) competitor; however, it is vulnerable to the toxin-encoding virus-Shiga (Stx) the bacteria carry in their DNA (shown right in picture).


The bacteria may carry around these viral hitchhikers because the Shiga toxin (Stx) gene might give the bacterial host an equalizer against bacterial predators, like Tetrahymena. To test this idea, reasearchers exposed an E. coli stain that did not carry the Shiga toxin to the eukaryote, Tetrahymena and as predicted, the bacteria were eaten. Whereas, when the bacteria containing the toxin-encoding virus- Shiga, some produced the toxin and killed the Tetrahymena; therefore, allowing the remaining bacteria to spread because there were fewer Tetrahymena eating them.


The Shiga toxin kills by binding to a receptor on the surface of a Tetrahymena and performs endocytosis to release the toxins, which cause irreversible damage to ribosomes and thereby promoting cell death. The bacteriophage induces the toxin release due to the presence of Tetrahymena by activating an S.O.S response. Scientists are working on identifying the danger signals involved in triggering the response, which can have implications for treating patients.


"When you give antibiotics to patients infected with the Shiga-toxin-producing bacteria, it may make them even sicker" he said. "That's because in the process of killing off the bacteria, the SOS response causes even more toxin to be released to do even more damage."


In recent studies, the Shiga-toxin was not effective at killing some Tetrahymena's, due to the development of resistance of the toxin by the Tetrahymena; therefore, there may be a treatment method that would give human cells the ability to become resistant to the toxin, too.


Researchers believe that the microbial war between the bacteriophage and their predators may play a role in the treatment of patients with this toxin.


"We have a very mammalian way of thinking about this and it's wrong. We are a very small part of the entire ecology of the planet and just because something can hurt us doesn't mean that's why it's there."


Sources:

http://www.cdphe.state.co.us/dc/Epidemiology/stec_fs.html

http://www.eurekalert.org/pub_releases/2007-12/asfc-hnt112807.php

http://www.sciencedaily.com/releases/2007/12/071203103405.htm


Image:

http://www.sciencecentric.com/news/07120316.htm

1 comment:

Lydia said...

"....bacteriophage (bacteria that carry a virus) competitor"

A bacterium carrying a bacteriophage is a not a bacteriophage. The bacteriphage is the VIRUS that is infecting the bacterium.