Reflections on my personal bacterial companions

I stopped a puck the other day.

With my leg. That's what comes with playing against these dad-gum college kids. They don't know their own strength.

The hematoma became infected, and since antibiotics aren't what they used to be my personal physician/spouse recommended diligent attention. So now the infection is mostly better.

This gave me the opportunity to wonder about three things:

1. Who creates the tough sealant (scab) atop the wound? I used to think my body did that, but, really, it's a stupid response. I need the sucker to drain, not seal. Maybe the scab is built by the bacteria?
2. Why don't infected wounds hurt more? I whack my finger and it sure hurts, but my body doesn't complain much about infections. Seems illogical ... unless the bacteria are turning off pain signals.
3. We know Toxoplasma makes rats dumb and happy - the better for cats to munch 'em and spread the infection. We think it does something similar to humans. So shouldn't bacterial infections make us feel kind of laissez-faire, less prone to aggressively treat the infection?

That was yesterday. I was inspired in part by a gruesome science fiction story of some years back about emergent sentience in bacteria (can't remember author, but I don't think it was Greg Bear).

I don't think these are original ideas, but I didn't expect to see a Carl Zimmer essay on the topic today!

I For One Welcome Our Microbial Overlords | The Loom | Carl Zimmer | Discover Magazine

.... Very often, the parasites cause hosts to do things that help the parasites, instead of themselves. For example, a protozoan called Toxoplasma needs to get from rats to cats, and to help the process along, it makes rats lose their fear of cats. Parasites can also change the diet of their host as well as the way in which their hosts digest their food....

I was reminded of this sinister manipulation by a paper that was published in Science today by Rob Knight and his colleagues. They built on previous research that revealed that mice genetically engineered to be obese have different kinds of microbial diversity in their guts than normal mice...

... Knight and his colleagues discovered a different–and more disturbing–way that microbes can make mice fat....

... Mice with a genetic make-up that alters the diversity of their gut microbes get hungry, and that hunger makes them eat more. They get obese and suffer lots of other symptoms. Get rid of that particular set of microbes, and the mice lose their hunger and start to recover. And that distinctive diversity of microbes can, on its own, make genetically normal mice hungry–and thus obese, diabetic, and so on.

When I first learned of this work, I asked Knight–with a mix of dread and delight–whether the microbes were manipulating their hosts, driving them to change their diet for the benefit of the microbes. He said he thinks the answer is yes...

If gut bacteria can change diet, then skin bacteria could make people with chronic skin infections apathetic -- the better to discourage treatment of the thriving bacterial colonies ...

Update 3/24/2010 - See also a 2006 post on viruses changing dietary behaviors ... Why would a virus fatten an animal?