PiU (samedi) wrote,

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sixth speaker

Having missed the opportunity to view several interesting guest speakers since my last outing into the world of academia I was finally able to put things right earlier this afternoon. The title of today's lecture was "How To Become A Pathogen: Lessons From the Pathogenic Eschericha" by Dr. Thomas Whittam of Michigan State University's Microbial Evolution Laboratory. The major emphasis was placed on the evolution of E. coli from a benign bacteria living in the gastro-intestinal system to a virulent pathogen capable of surviving in bovine reservoirs and passing along infectious diseases between humans.

Most of the discussion on gene-mapping was outside my knowledge of biology, but there were a few things about the O157:H7 strain of E. coli that caught my interest. One of the main discoveries was a formula concerned with the natural selection forces in operation for pathogens, which concentrated on a corresponding relationship between enhanced rates of transmission and lowered virility. It makes sense though, as one of the best ways to ensure you pass on your genetic material is to avoid detection for as long as possible by keeping your host unaware of what you're doing.

There are several species of Eschericha that cause dysentery, but the predominant strain, O157:H7, is actually most closely related to 055:H7 - an intestinal bacteria that is found almost exclusively in children and which doesn't cause bloody stools like it's nearest relative. E. coli and other Eschericha species have acquired toxicity independently of one another through the production of Shiga (Stx) toxins and special plasmids (acquired in subsequent stages), as well as developing the ability to move from humans to ruminants (such as cattle) over time.

This probably isn't a topic covered in most general education or high school classes, so it was interesting to hear how Eschericha started off as commensal genus that didn't harm its human host before evolving into the modern fright that it is today. With the recent concern over SARS and Avian Influenza A/(H5N1) it's worth realizing that there are some pathogens that have attacked us first before moving on to other species in the animal kingdom.

Plus, there was also a humorous moment during the Q&A session, when one of the university's faculty members asked about the origin of E. coli's pathogenic state - Dr. Whittam's reply was, "Well, looking at it with our molecular clocks we've managed to narrow the date down considerably. Mapping the genome has given us a starting point of 30,000 years ago, while the first identified infection in a human can be traced to 1975. So I'd be willing to bet it took place some time between 30,000 years ago and 1975. You have to admit, for evolutionary biology that's pretty good!"
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