mutation

[MIA6]

In my book, it says, Doctor may refuse to give you an antibiotic for a mild illness because he/she may not wish to risk your developing a resistant strain. It sounds more like Lamarck’s theory that because your body wants to resist penicillin, then it develops a resistant strain. But Lamarck was wrong. According to Darwin, it should be a mutation just happens naturally, so even if your doctor gives you a lot of antibiotics, if the mutation doesn’t happen, then there is no point of not giving you antibiotics. Suppose your doctor just gives you antiobiotic once, then you have mutation, it’s a random chance of developing a resistant chain.
Thanks for help.

[blcr11]

Maybe I misunderstand you. It sounds like you’re saying that "you" (the patient) mutate in response to antibiotic. That’s not the case. Giving you an antibiotic kills off the susceptible bacteria, but selects for resistent strains that are not affected by treatment. The resistence "mutation" in all probability already existed in the population of the infecting bacteria. By treating an infection that could just as easily be handled by your own natural immune mechanisms, you may be encouraging the spread of resistent strains of bacteria. This is becoming a serious problem. The overuse of antibiotics has helped create strains of Tuberculosis and Staph, for example, that are resistent to almost anything now availble.

[MIA6]

Hi,blcr11, thanks for your explanation. So you mean antibiotics make us develop a resistant strain? but according to Darwin, it’s wrong. For an example, a giraffe’s neck becomes longer because he has to reach the tree to get food, that’s why it becomes longer? I mean that mutation should develop in ourself naturally, it shouldnt be influenced by antibiotics.

[david23]

There is no mutation occurring in blcr’s reply. Lets just get one thing clear, there is not going to be a mutation with the bacteria living inside of this particular sick person, I’m just stating that so our discussion can become easier. There could be, but we are ignoring it. The resistant strain probably already exists but cannot take over the body because it has to compete with other nonresistant bacteria. The antibiotics will eliminate the nonresistant ones, leaving the resistant ones to grow and eventually overwhelm the body.

[blcr11]

It’s about as Darwinian as I can imagine. We don’t induce anything. There are individual bacteria already present in the population that are more fit for growth in the presence of antibiotic. They have a selective growth advantage over those that are not resistent, and are therefore selected by antibiotic treatment. It’s survival of the fittest. Now, if we don’t treat with antibiotic, there is no selective pressure exerted and the resistent strains have no better chance of survival than the non-resistent ones, all other things being equal.

[kotoreru]

Indeed, resistance can actually confer a selective disadvantage in the absense of antibiotics.

[fulmenatrum]

From what I understand is that once you are given such a treatment like antibiotics, then the cells that have no resistance to it dies away. But usually, there are some mutated cells in the population that are already immune to this disease. So what this antibiotic does is it ‘selects’ the cells immune to the virus already which then lets the mutated cells reproduce resulting in a population of new cells that are immune to the disease. But the thing about this is that some things such as colds have a protein coat which change the way they look so that the antibodies can’t recognize it. That’s why there aren’t any vaccines or specific medicine to cure colds since the cold is always changing its structure.

[canalon]

quote fulmenatrum:

From what I understand is that once you are given such a treatment like antibiotics, then the cells that have no resistance to it dies away. But usually, there are some mutated cells in the population that are already immune to this disease. So what this antibiotic does is it ‘selects’ the cells immune to the virus already which then lets the mutated cells reproduce resulting in a population of new cells that are immune to the disease. But the thing about this is that some things such as colds have a protein coat which change the way they look so that the antibodies can’t recognize it. That’s why there aren’t any vaccines or specific medicine to cure colds since the cold is always changing its structure.

Ouch that is a mess of a comment. You are mixing up bacteria, cells diseases and viruses in an awful mess.

So to make it clear:
You have bacteria living in you, some permanently, some more transiently (the latter ususally includes the one that you will receive antibiotics for). There is ahuge diversity among those bacteria, notably in the case at hands in terms of sensitivity to antibiotics. Some will be fully resistant, some will be fully sensitive and some will just see their growth survival compromised. The different level of resistance can come either by the presence of pre-existing resistance genes (which are not always counter selected, but that message is already too long to give more details) or because some mutations confered resistance to some part of the bacterial population. When you take the antibiotic, all the sensitive bacteria in the population that get exposed to the antibiotic will die, and the resistant population suddenly has plenty of ressource available and take over. So the frequency of resistant strains increase in your population, and you now start to shed mostly resistant strains, which can in turn get into the rest of the community. As blcr11 said, nothing but darwininan selection here.

But your cells are not disseminated, and are resistant to the antibiotic (otherwise it would kill you too), so whatever happenes to your cells is not relevant. And antiviral molecules have completely different modes of actions, and usually have side effects that are not really worthy to fight a cold (but much more to fight AIDS for example), that is why in some case it is better to let your immune system handle things.

[david23]

lets not use the word mutate so lightly. After all bacteria dont like mutation either. Viruses on other hand have enzymes that purposely create variations in their genes, or lack error proof mechanisms unlike bacteria and of course humans.

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