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The problem is that there was a very compelling "just so" story that antibiotic-resistant bacteria are inherently at a competitive disadvantage vs. susceptible
by Fomite 5y ago
The problem is that there was a very compelling "just so" story that antibiotic-resistant bacteria are inherently at a competitive disadvantage vs. susceptible bacteria absent selective pressure.
Take the antibiotics away, and the resistant bacteria will follow.
Unfortunately, microbial ecology is much more complex than that, and it hasn't panned out that way. Often because resistance plasmids also carry other helpful genes. For example, I'm currently working on a study where there's high levels of antibiotic resistance to an antibiotic that isn't used in that population because there's other things hanging out on the same plasmid.
Also note: That's not what most people mean when they say "ecological fallacy", which is a statistics term.
- jessriedel 5y agoNot all proposed evolutionary mechaniams that turn out to be false, much less merely incomplete, are just-so stories. The fact that the hypothesis was simple makes it more reasonable.
- Fomite 5y agoYeah, but this was very much a just so story.
- jessriedel 5y agoHuh, how? It takes scarce resources for the bacteria to produce many of the structures that protect it from antibiotics. Structures that are unused but require resources are selected against, or at the least decay through mutation. This is an extremely common and simple evolutionary effect. Are you using "just so" as a synonym for "suspiciously convenient"? That's not what it means.
- Fomite 5y agoNo, I'm using it to mean an untestable (or in this case untested) narrative explanation for a biological phenomenon. There are several prevalent narratives around the evolution of microbes that are taken to be true because they tell a nice narrative story with very little empirical backing, and even less information on things like time frames. "Structures that are unused but require resources are selected against" for example, is something that feels correct, but isn't necessarily true because resistance genes don't exist in isolation. "Community MRSA will lose out to MSSA because of an absence of selective pressure" kept being trotted out because it fit narratively well beyond when it was becoming apparent that wasn't true.
- jessriedel 5y agoI can't find a way to interpret your use of "narrative" that makes your argument work.
- quotemstr 5y agoThe explanatory gap you're seeing is the difference between equilibrium and dynamic analysis. As time goes to infinity, the probability of an organism retaining genes not useful to it declines to zero. Given enough time, that resistance gene, if not directly beneficial by side effect, will be pruned. But evolution takes time. If the resistance gene is on a stable plasmid, if the plasmid confers other fitness advantages, and if the resistance gene itself only infinitesimally reduced fitness, then evolution can take a very long time indeed to reconfigure that plasmid and optimize away the resistance gene. Both camps are right here.
- Fomite 5y agoThe problem is one of those camps was relying on an equilibrium condition and pretending like it was on a clinically relevant time scale.