A superbug is a strain of bacteria that has become resistant to antibiotic drugs, according to Oxford Dictionary. The reason that it can resist the drug is because it has evolved in the environment which contains the drug. Only those that contain the drug resistant gene can survive and become the superbug.

But why don't they become weaker after the evolution?

I have this question because I once worked with the resistance of HIV to lopinavir drug. There are mutants of HIV that can resist the drug, however, after the resistance, the structure of the virus itself is more fragile, hence they're weaker than the wild type. This seems logical because in its ordinary environment, the wild type of virus should be the strongest one. Any mutation of it is to fight back the drug, hence it is not the strongest one anymore.

I know that my only true for HIV, a virus, not bacteria. But I don't understand why this logic cannot apply to them. Based on the alarmed of many resources, superbugs are stronger than their wild type. Do you know why superbugs aren't weaker than their wild type?

  • @CareyGregory, YviDe - please don't answer in comments. Clarification is fine (e.g. "What do you mean by 'weaker'?") but an answer is not. Thanks. – anongoodnurse Nov 21 '15 at 7:41
  • Please see meta question about comments with downvotes. You're not likely to get one, even if you ask. – anongoodnurse Nov 21 '15 at 7:44
  • @anongoodnurse I don't think that question is related to me. See my comment there. Also, I think that the meta post explains why answer in comment is prohibited should be link – Ooker Nov 21 '15 at 10:01
  • My guess is that "Based on the alarmed of many resources, superbugs are stronger than their wild type. Do you know why superbugs aren't weaker than their wild type?" You have provided no sources for this difficult claim. Naming your (re)sources (excluding the Oxford dictionary, which is an excellent source on English Language and usage) with a pertinent summary usually makes for a much better question. – anongoodnurse Nov 21 '15 at 10:15
  • @anongoodnurse I read them on newspapers in my native language. They are credible sources in my country (like The NY Times), but what they written in are just short interviews with doctors. Being said, I think this is widely accepted knowledge. Do you think that I really need to have an English resource? Also, why the dictionary shouldn't be a resource for definitions? – Ooker Nov 21 '15 at 10:34

(This answer is related to my answer on Bacteria resistance to natural antibiotics on the Biology SE)

First of all: When it comes to evolution, Biology doesn't talk of 'strong' and 'weak' , it talks of 'fitness' ("survival of the fittest", for example), which is about how well adapted to their environment an organism is. Fitness includes how well it can survive in its environment and how much it can produce vital offspring.

This seems logical because in ordinary environment, the wild type of virus should be the strongest one. Any mutation of it is to fight back the drug, hence it is not the strongest one anymore

This is a misunderstanding of evolution. The wild type of a species is not the fittest this organism can be. That it is the wild type just means that it evolved and spread. Something that doesn't evolve can't spread (as an hyperbolic example, it might be advantageous for humans to have wings, but since we didn't evolve it, our wild type doesn't include it).

It also helps to remember that "the wild type" is not a uniform thing. There are many genetic variations which we still consider to be the wild type. Even bacteria that reproduce through asexual reproduction are not all the same, even within one host.

In the natural environment of the bacteria you are talking about, an antibiotic resistance confers little benefit because they don't encounter it. So if it evolves, it won't help these organisms survive and would only spread throughout the population by chance. On the contrary, it might even confer a disadvantage - for example, penicillin resistance required producing the protein beta-lactamase. In a penicillin free environment, this might just be a costly extra without a benefit. Over time, it might get lost.

In a human taking antibiotics, however, these bacteria with an antibiotic resistance are indeed fitter and have a survival advantage. Bacteria with multiple resistances even more so. Between bacteria, these resistances can actually be transferred by something called "transformation" that involves actually picking up genetic material, so evolving multiple resistances also isn't as uncommon as it may seem.

As for your virus example, without knowing more, I'd guess that the fitness reduction in the more resistant virus strain is probably a side effect of the resistance. Getting more or less fit through evolving resistance to treatment is not, in itself, a difference between viruses and bacteria.

Origins and Evolution of Antibiotic Resistance

Mechanisms of Bacterial Resistance to Antibiotics

What is fitness?

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  • I think the terms stronger and weaker (though I agree with your answer) sort of perpetuate a misunderstanding. Maybe discuss in terms of advantages in niches? I'm not sure exactly how to address it except in that way. And the cost to the bacteria which develops an antibiotic resistance is a great point. – anongoodnurse Nov 21 '15 at 7:38
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    @anongoodnurse tell me about it... My native language actually does translate "survival of the fittest" with "survival of the strongest" which leads to even more misunderstanding. I put the part about strong and weak being the wrong words at the beginning. – YviDe Nov 21 '15 at 7:57
  • Ouch... that really does not fit with bacteria, does it? lol! – anongoodnurse Nov 21 '15 at 8:17

In short, because mutations are not defined as specific.

A mutation of any bacteria could be mutation that could be weak or strong.

Weak & Strong would be quantified by our technology, treatments and comprehension of the bacteria.

There are two factors important to understanding the change of the bacteria.

Epigenetic Adaptation (No Genetic Mutation)

Genetic Adaptation (Genetic Mutation and Selection)

Bacteria can acquire large pieces of DNA from other bacteria, viruses and the environment.

How Does Selective Pressure Impact Antibiotic Resistance?

In order for a gene to remain functional and a part of the bacteria’s genome over an extended period, it has to help improve the survival and/or competitiveness of the bacteria. If a gene stops being helpful it will eventually become non-functional and will be removed from the genome. This means that the development and maintenance of antibiotic resistance is usually dependent on the bacterial population being frequently exposed to non-lethal doses of the antibiotic (note: some bacteria are intrinsically resistant to particular antibiotics). This process eliminates those bacteria that have lost resistance, and increases the percentage of resistant bacteria. In real life, this means that antibiotic resistance is likely to emerge in environments where bacteria are frequently exposed to antibiotics. On an individual level, this means that a person is more likely to develop an antibiotic resistant infection from undergoing long-term or prophylactic antibiotic treatment, as opposed to short-term antibiotic treatments of acute infections. This also means that bacteria may lose resistance to antibiotics that are no longer frequently used.

Check out This Article for more information.

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  • Wow, nice article! Thanks! – anongoodnurse Nov 21 '15 at 7:40

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