19 January 2009

Are *you* a germophobe?

I have a feature in the new February edition of SELF Magazine. (For readers outside the US, SELF is one of the largest magazines aimed at women 18-40 — and it has a ton of international editions, so it may well be on your newsstands too.)

It's titled "Germophobia," and it's a light-hearted but also serious look at how we can live without paranoia in a microbial world.


daedalus2u said...

That is a nice article. Touched on just about everything. Not quite as pro-commensal bacteria as I would like, but I suspect the audience you were writing for wouldn't appreciate what I would want to say. Since I read up on the hygiene hypothesis and in the context of my research, I don't worry much at all about germs. I rely on my NO generating commensals to protect me.

One thing you left out was the degree to which normal commensal bacteria protect from pathogens by interfering with them. The normal commensals increase the numbers of bacteria needed for an infective dose. If you increase the dose required for infection above the number you are exposed to, an infection doesn't happen. That is a very large part of what the normal commensal do, and why many times infections (such as yeast infections) follow antibiotic use. That is quite well documented in vaginal flora where Lactobacilli are quite important. An important strain, L. crispatus which generates hydrogen peroxide as well as producing a low pH (~4).

One of the things that makes MRSA so deadly is that it is resistant to many antibiotics that normal commensal bacteria are not resistant to and those bacteria normally suppress the MRSA. If you are colonized with MRSA but the MRSA is kept in check by normal commensal flora (the usual case); then an antibiotic will wipe out the normal flora but doesn't wipe out the MRSA, then with the open niche and all the normal commensals gone, the MRSA can expand, express quorum sensing compounds, express virulence compounds and cause a truly virulent infection extremely rapidly. Wiping out the normal commensals has lowered the number of MRSA needed for an infection.

The patient mentioned in the other item who became colonized with MRSA wasn't "infected" because the MRSA wasn't expressing virulence factors and was below the threshold that produce an "infection" because they were kept in check by something; skin commensals, skin pH, skin dryness, the immune system, or something else. Remove that something (as in the media containing cefoxitin did) and they grow rapidly.

I think that one of the reasons the body produces so much NO during sepsis is that low NO is used by bacteria to trigger biofilm formation. High NO suppresses biofilm formation and the last thing you want if you have bacteria floating around in your blood stream is for them to attach somewhere and generate a biofilm. Eradicating them then (in the wild) becomes nearly impossible.

Maryn McKenna said...

Thanks for the reaction, Daedalus. It's funny: That article grew by more than 1,000 words over what the magazine originally wanted, because they found the science (especially of the hygiene hypothesis) fascinating. And yet there still wasn't room to talk about everything! I absolutely agree that commensals are an important part of this equation, and also not well understood by most of the public. It's yet another expression of our lack of science literacy as a population, that we somehow see ourselves as sterile beings attacked by a pathogen, rather than understanding that we host collections of microbes and live in a world of microbes.

daedalus2u said...

It is not well understood by researchers or clinicians either. I am having a terribly difficult time getting anyone interested in the commensals I am working with. There is interest in gut commensals, interest in commensals in every other cavity, but next to no interest on the external skin.

When I have talked with people looking at skin commensals, they are only interested in "scientific", "reproducible", "random" samples, not samples from someone who has (seemingly) developed a stable biofilm and has not bathed in years. To me, that would be the most interesting type of skin commensals to look at, those which are stable and resistant to being displaced.

That is really what you want, a stable biofilm of something harmless (or helpful) that suppresses everything else and which actively resists being displaced. That is better than wiping the niche clean periodically and allowing random invaders to recolonize. The recolonization is a stochastic process which depends on what you are exposed to. If you are exposed to MRSA, eventually it may take hold. Trying to live in a sterile bubble isn’t going to work.