how does not finishing a course of antibiotics cause antibiotic resistance?
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When the symptoms go away it doesn’t mean that all the bacteria are dead, just that they are suppressed and aren’t actively harming you because they are too busy with trying to survive. If you haven’t finish the course then chances are you haven’t killed them all. So the survivors will spend some generations in antibiotic-saturated environment. In this environment mutations which provide for antibiotic resistance will be highly beneficial, so the surviving bacteria might evolve this trait. Then your infection will come back with a vengeance.
In a large population of bacteria, some are a bit more resistant to antibiotics than the rest. You can still kill them with a lot of antibiotics for a long time, but they survive small amounts unusually well.
If you stop a course of antibiotics early and your infection comes back, the new population of invading bacteria started from the most antibiotic resistant individuals that were in the last infection. That means the new population has a leg up on developing complete immunity to the antibiotic you used.
Think of it like a game of tag. The antibiotic needs to tag all the bacteria to win, but that takes time. You will stop feeling sick when most of the players are gone from the field, but that just means the ones left can figure out how the person who is “it” works. If you don’t eliminate them too, they can join new games of tag on other fields and now they have strategies on how to avoid getting caught.
It’s not a perfect metaphor, but I think it covers all the main points.
If you take most of the antibiotics but stop early, it might not kill *all* of the bacteria you’re infected with. Maybe 90% of them die, so you feel better, but 10% are left alive.
…but not just a random 10% survived. It’s the 10% that are most-resistant to the antibiotic. So now your body is carrying bacteria *that aren’t as easily killed by that antibiotic*, and you can pass those out into the world where they can infect other people. And those people will find that antibiotics don’t work very well for them, since they’re infected with ones that are all descended from the resistant ones you let escape instead of killing them. So now they need a bigger dose of antibiotics.
After many cycles of this, bacteria get more and more resistant, and can eventually become completely immune to a given antibiotic. Which is *really* bad because we only know of so many antibiotics and it’s really hard and expensive to come up with new ones. And if we run out of antibiotics, the treatment for an infection is going to become amputation again like it was in the old days.
If you don’t kill them all the ones that survive will know all your battle tactics and their descendants will come back with evasive maneuvers
Im curious. How do doctor determine how much antibiotics needed for certain illness? What happened if it is not enough?
“Only the strong survive”.
Poor prescribing and patients not finishing courses can cause antibiotic resistance but it’s a small impact in the big picture.
Antibiotic use in agriculture has fucked us.
Let’s say I’ve got a flower bed in my garden that has been infested with weeds. Say I decide to spray them with a weed killer herbicide every day. The instructions on the bottle say I have to spray every day until the bottle is empty. I notice after a couple of days that most of the weeds in my garden are dead but there are a few herbicide resistant weeds left. They’ve been weakened by the herbicide but they aren’t dead. If I stop spraying them before they’re all confirmed dead the resistant weeds will repopulate and they’ll be even harder to kill the next time around and I’ll need a stronger and more harmful weed killer next time around.
Newer information has come to show that may not be entirely correct.
The article below points out that “Most of us were taught that terminating antibiotics prematurely can lead to the development of bacterial resistance. This has proven to be a myth as mounting evidence supports the opposite. In fact, it is prolonged exposure to antibiotics that provides the selective pressure to drive antimicrobial resistance; hence, longer courses are more likely to result in the emergence of resistant bacteria. Additionally, long durations of therapy put patients at increased risk for adverse effects.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5661683/
The WHO notes that
“Evidence is emerging that shorter courses of antibiotics may be just as effective as longer courses for some infections. Shorter treatments make more sense – they are more likely to be completed properly, have fewer side effects and also likely to be cheaper. They also reduce the exposure of bacteria to antibiotics, thereby reducing the speed by which the pathogen develops resistance.”
https://www.who.int/news-room/questions-and-answers/item/antimicrobial-resistance-does-stopping-a-course-of-antibiotics-early-lead-to-antibiotic-resistance
See also
https://bpac.org.nz/BPJ/2015/June/symptoms.aspx
You can be infected by many things without showing any symptoms – your body doing is thing by controlling and suppressing the problem.
This means that if you stop taking an antibiotic at the point you feel better, you may still be infected, just with a lower dose that your body is capable of handling.
This leaves behind bacteria that have potentially been exposed to the antibiotic, but not killed – giving them a chance to mutate and adapt to resist it. Ideally this will then just be killed off by your bodies natural defences, but if some survive and manage to infect someone else, you now have a strain that is slightly stronger and more resistant.
If you complete your full course of antibiotics, it should hopefully have been prescribed to last long enough as to reliably kill off the bacteria fully, and not leave any significant amount behind.
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