Comment by ronaldx | Hacker News Reader

Comment by ronaldx | Hacker News Reader

> Eventually bacteria will evolve, and they’ll adapt ways around that to overcome that obstacle.

I am more optimistic than that.

Sure: as long as antibiotic resistance is crucial for bacterial survival, bacteria have a natural need to evolve it. And, they will.

But, this will come with a genetic cost to the bacteria.

The reason that antibiotics work is because they are attacking some function that has deliberately evolved, through natural selection, to be like that. Antibiotic resistance must literally cost bacteria some efficiency in some of their other functions.

This cost was originally such that the bacteria would die. Fantastic. But note: we wouldn't actually benefit from all bacteria dying at the mention of the word antibiotic, and some bacterial resistance is good for us.

Under normal circumstances, bacteria that don't need to carry around antibiotic resistance with them will most likely have a lower genetic cost and thrive better. This may be why we have seen MRSA predominantly in hospitals and rarely in the 'wild'. (If MRSA was necessary or not costly, all SA would be MR all the time).

This gives me some hope - that antibiotic resistance is balanced, genetically forcing bacteria to be less effective in other ways and less competitive in other circumstances.

We humans are not out yet.

>The reason that antibiotics work is because they are attacking some function that has deliberately evolved, through natural selection, to be like that. Antibiotic resistance must literally cost bacteria some efficiency in some of their other functions.

I'm not convinced that there must be a cost; furthermore, I think it's unlikely that if there is a cost, it is high enough to be significant. Bugs evolve, but they do not necessarily evolve optimally all of the time. It is possible that an evolutionary step towards resistance might also improve the fitness of the germ overall (for example, by further optimizing the efficiency of a metabolic pathway). That evolutionary step might have been inevitable, but required additional selective pressure or the presence of a more active mutagen to actually occur.

Your claim is sort of assuming that each bug is already optimal for its environment, and any change must therefore be deleterious in some regard, but I hold that neither fact is necessarily true.

I appreciate your point and I don't disagree with you (+1). However, the issue is complicated and I wanted to present another side to the original post.

I think it's likely that those two claims are mostly true in bacteria. Since bacteria evolve quickly and have experienced a lot of evolution, I believe they are likely near-optimum and therefore the second claim (IMHO) follows from that: changes would typically be deleterious.

On the other hand, even allowing for that, it's possible we could be allowing them to escape a local maximum and reach a more-optimal state.

And, there is a more significant criticism you could make:

Even if I am right on both points, a population that evolved to be heterogeneous (with some small percentage of wildtype being resistant) could likely have the best of both worlds ;)

http://en.wikipedia.org/wiki/Plasmid

"In nature, plasmids carry genes that may benefit survival of the organism (e.g. antibiotic resistance),"

Plasmids cost energy, they are dropped in the course of natural selection if they stop conferring an advantage.

More quickly than you might think, too.

If we stop using antibiotics, the bacteria will become less resistant.

Plasmids are only one of the ways that bacteria adapt.

Adapting antibiotic resistance can take as little as a single nucleotide mutation in the right part of a bacterial genome. Many of the known antibiotic resistance mechanisms involve small mutations to critical proteins.

Norway did just that, and it seems to have worked rather well.

http://www.cbsnews.com/2100-205_162-6014559.html

There is a catch here however, any resistance a bacteria has, has implicit cost to the bacteria in the form of copying the resistances' dna into new cells. This costs the organism energy and time to copy. If it confers no benefit it will be dropped from the genome.

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Bacteria both evolve resistance quickly, they also lose it just as quick. Because unless it directly is needed in the here and now, the bacteria that remove it and survive without it outcompete the rest of the bacteria.

This is my understanding at least, a real bacteriologist can comment what I inevitably got wrong. But the recent study that used existing antibiotics in a certain way to kill bacteria is a great demonstration of bacteria not being able to select for all simultaneously and retain the old resistance in the future.

I'm not overly concerned about bacterial resistance given there are ways we can work around it.

> Bacteria both evolve resistance quickly, they also lose it just as quick.

Alas, experiments have shown that it is possible for resistant strains to strongly reduce the cost of resistance maintenance. If there are no naive invaders, this can lead to an evolutionary stable situation where the maintenance of resistance is less costly than losing it.

See Lenski's (old) review "Bacterial evolution and the cost of antibiotic resistance"

This makes the assumption that evolution results in a perfect organism, which it does not. Instead, it results in a "good enough" organism.

The definition of "good enough" for bacteria has changed over the last 50 years, so these changes are occurring now. It doesn't necessarily require a cost, or at least not a cost that matters to humans.

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