bacteria


Sometime last year, on his now-defunct tumblr feed, Recursive Muffin, Ethan Mitchell asked a question I thought the folks on This Week In Microbiology (which I’ve written about here and here) might be able to answer. I emailed them and they did so, at the end of episode 73. I thought the question and answer were interesting enough to transcribe here:

Question of the day: A strain of Flavobacterium (KI72) evolved the capacity to digest nylon, obviously in recent history. Fine and well. How long will it be until one of the cariogenic bacteria species evolves the ability to digest dental resin? After all, we are putting a lot of it on their dinner table.

Answered primarily by Michael Schmidt, who teaches microbiology to dental students at MUSC, with help by Michele Swanson and Vincent Racaniello. Keep in mind that this is a transcribed conversation, so informal, and that I don’t know how to spell some of these words:

Michael: This has already happened to some extent. In the United States we currently spend 5 billion dollars a year replacing resin-based composite fillings due to failure. The average lifespan of a resin-based filling that a dentist will put in today is around 6 years. And the recurrent decay usually compromises the restoration earlier in its lifespan, and that’s when the bacteria are effectively going after the “glue.” And they’re going—because it’s a polymerization and the microbes—if the restoration isn’t properly fixed and properly cured there’s enough carbon in there that they can get at before the polymerization is completely done, that they can actually get after it. And then afterwards, matrix metalloproteinases and cathepsins places the longevity ceiling at that 6 years, even at healthy and bacterial free restorations. And so these matrix metalloproteinases and cathepsins which are expressed specifically in dentin, they come in and they cause the restoration to fail.

Michele: But those are bacterial, Michael, or those are…

Michael: No, those are eukaryotic. The bacterial failure… places the longevity cap at around 6 years, so there’s currently a resin-based product in the market that’s from a Japanese company that puts chlorhexidine into some of these resin-based products in order to prevent microbial attack and to take out the… bacterial attack. So we’ve been looking at copper nano-particles to effectively prevent some of this decay, but what he is hypothesizing has already been happening in the US and it happens throughout the developed world, anyplace people are using resin-based fillings. The old silver fillings typically last 25-30 years without incident. Most people were concerned about the mercury issue but the amount of mercury in an amalgam based filling is insignificant in terms of health consequences if you look at the evidence-based literature. It really has no issue associated with the health of the individual.

Michele: And I don’t suppose there’s any data saying the half-life of the resin is decreasing? Which would be consistent with this idea that we’ve selected for bacteria, we’re enriching for bacteria, that can break it down more readily?

Michael: No, because the resins have gotten better. The polymerization agents and the curing times, so we don’t have a clean experiment to do it. The folks haven’t actually looked to see if resin-based dissolving bacteria… but that’s a question that I can ask my friends at the Forsyth Institute to see if they’ve hunted to see if there are any resin-eating bacteria out there. But it’s all about the polymerization because the polymer needs to be perfectly cured and any of you who’ve had a recent composite filling you remember the dentist putting on the dark glasses and giving you a pair of dark glasses and they put the magic light into your mouth to cure the filling. And typically they only put the UV lamp in there for 20-30 seconds and that’s what starts the curing process. And we’ve all made polyacrylamide gels and it’s a variation of polyacrylamide gels except we use… Temid and whats the inorganic… the inorganic salt. I haven’t made a gel in…

Vincent: I can’t remember either.

Michael: Because you just pull MP… not MPS…

Vincent: APS

Michael: APS. Ammonium persulfate and that’s what goes bad. The binary catalyst.

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In his new lecture for the Long Now Foundation, Geoffrey West asserts that part of the problem humans face is that we tend not to understand exponential growth. An economy growing at a miserable 2%, for example, is still growing exponentially. And economic growth is still largely a measure of the acceleration of entropy–how much faster are we turning resources into pollution. He advises figuring out ways that periods of slow or no growth OK, because it will have to be.

Exponential growth really is counterintuitive. Here’s the way he describes it:

Imagine you are going to grow a test tube of a bacteria, starting with one bacterium at 8 AM and ending with a full test tube precisely at noon. The bacteria grow by doubling–a kind of exponential growth–each second. So at the end of one second we have two, after two seconds we have four, after three seconds we have eight, and so on. That being the case, at what time will the test tube be one-half full?

Right. Precisely one second before noon. And two seconds before noon it’s a quarter full. Three seconds is an eighth, four seconds a sixteenth. At 11:59.55 AM, the tube is only 1/32 full. Imagine being a bacterium in the tube at five seconds to noon. It would seem more crowded than usual, but look at all that space to go, and we’ve been doubling like this for almost four hours! There may be a problem in the next few days, but certainly not in the next few seconds–exponential growth is probably also counterintuitive for bacteria.