Wednesday, July 30, 2008

Cryptosporidium, Antibiotics, and Doodie in the Pool

The WSJ reported yesterday that you should be wary of swimming in a public pool these days. Seems that there have been several outbreaks of illness with people who were swimming in a pool. The cause was found to be a bacteria called cryptosporidium. At first glance, you might find yourself laughing, thinking back to the famous scene of Bill Murray in Caddyshack (one of the all time great movies) biting into a Baby Ruth bar after cleaning the pool. Or your might ask, why the heck would the WSJ pick this story up?

Well the significance of this story is more related to why there haven’t been outbreaks in the past. Prior to these outbreaks, Cryptosporidium could not survive the chlorine in the pool. The fact that people got sick from this bacteria suggests that there is now a strain that is chlorine resistant. Wow, that’s a bit scary. Bleach is chlorine, and chlorine is a strong oxidizer, commonly used to kill germs, etc. Now while the concentration is of importance here, the bigger picture is that there is now a strain of bacteria that has demonstrated the ability to survive chlorine, where as in the past, it could not. That’s the definition of antibiotic resistance. While it’s sucks to think you are now swimming in a toilet, the implications are more far reaching.


Antibiotics are used very frequently these days to treat infections, etc. The thing about these new powerful antibiotics are that they are indiscriminate. They kill the bad bacteria causing the infection as well as the good bacteria that lines your gut. But most importantly, there are some bad bacteria from time to time, that figure out a way to survive the drug. Since bacteria in general replicate so quickly, they pass along this genetic mutation that gives them their resistance to subsequent generations. The bottom line is that if the evolutionary mechanism that the resistant bacteria develop is effective, then these bacteria will survive the subsequent antibiotic treatment.*

There is enormous research around antibiotics, and if given the choice, you should think hard about taking one. It’s really not that the bugs are better at generating genetic diversity and passing along traits that enhance their survivability any better than humans, or any other living organism. Their generations play out on a time scale much faster than ours, and this simple fact puts us at risk every time we take an antibiotic.

* For example, tetracycline used to be the antibiotic of choice, but bacteria developed resistance to tetracycline. Tetracycline entered into the bugs, and disrupted the bacteria’s ribosome. The ribosome makes proteins that are necessary for the bacteria’s survival; disrupting the ribosome keeps the bacteria from multiplying. The molecular biology basis for resistance to tetracycline is that the resistant bugs developed the ability to pump the drug out before it could disrupt the ribosome. Self-preservation on the part of the bacteria resulted in the ability to pump tetracycline. This trait was then passed on to subsequent generations (“survival of the fittest”). It should be noted that tetracycline is a bacteriostatic (keeps bacteria from replicating) versus a bacteriocidal (kills bacteria).

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