What do antibiotics do exactly and why do people grow resistant to them?


What do antibiotics do exactly and why do people grow resistant to them?

In: Biology

Antibiotics are basically just poison for bacteria. Different antibiotics work differently, some just prevent reproduction, others kill them directly.

The thing is that they don’t always kill all of the bacteria. Some will only meet a minor dose, or have a random mutation that makes them more resistent.

Statistically the surviving bacteria are more resistent, because those die last. And then they can pass on that feature to their “offspring”. I.E. the 0.1% survivors become a more resistant strain when they multiply again.

Antibiotics kill bacteria. Bacteria mutate and adapt to their environments (see evolutionary theory) so exposure that does not kill peripheral bacteria can result in mutations that make that bacteria more resistant to the antibiotic.

Hence people should be washing their hands with soap (surfactant to slough and rinse away bacteria) and minimizing the use of hand sanitizer, I think, but someone correct me if this inference is incorrect.

Antibiotics work in one of two ways
1. Kill bacteria
2. Stop or slow antibiotic from reproducing

People don’t become resistant to antibiotics, it is bacteria that gets resistant. It’s really a survival of the fittest situation..

Proper use of antibiotics is really important community wide, not just individual to individual.

Hi 🙂

> antibiotics do exactly

They are poison. Bacteria can not grow in poison and die, or at least grow slower so our immune system can win the battle more easily.

As they are “poison”, you get side effects.

The trick is to develop antibiotics that are very effective against bacteria, but don’t cause much trouble for our body.

The classic example: If you let bread sit in a petri-dish, it will grow fungus. The fungus produces poison. Bacteria can not grow where the fungus grows. (Flemming, 1928, discovered the effect of Penicillium notatum.)


> people grow resistant

People do not grow resistant to them, but the bacteria.

They multiply and sometimes some will survive. If these can multiply again, you get resistant strains eventually.

Especially if you stop taking the antibiotics prematurely (“I feel better so I don’t need the rest”). The decreasing amount of “poison” will allow more bacteria to survive, multiply more, get a higher chance to become resistant.

And then you’ll pass them on, if you’re going to work too early and without taking your medication to the end.


Bacteria reproduce rapidly. And if there’s some mutation (error when copying their “code” during reproduction) that can result in them being more resistant to the used antibiotics. Those will survive.

Existing bacteria doesn’t just get resistant. It’s their “offspring”. What can take thousand of years for animals, humans, can happen in a few hours/days with the rapidly reproducing bacteria.


Another issue is taking antibiotics without reason (e.g. some people taking them when having a VIRAL infection. Or chicken farms using antibiotics as precaution, just because it’s cheaper than dealing with a possible outbreak). This will increase the chance of some bacteria developing a resistance to that antibiotic.

Antibiotics kill germs that cause infections. But antibiotic-resistant germs find ways to survive. Antibiotics also kill good bacteria that protect the body from infection. Antibiotic-resistant germs can multiply.

People don’t get resistant to them. The bacteria these chemicals target do. Ideally an antibiotic won’t interact with the person at all. The bacteria becomes resistant because some small number are just naturally resistant and will live. They then go on to repopulate with this immunity now in the population. This is because they have a small difference in what the antibiotic targets (cell wall, reproduction cycle, metabolism process, or whatever it happens to be) so that the antibiotic can’t interact with the systems it was designed to. Think about it like a key and lock. You change out a single pin on the lock and the key fails to work anymore even when the lock itself works perfectly fine still. You now need to make a new key to open the lock or in this case kill the microbe.