Biology Question?

[nickhooker22]

How does Natural Selection act to make bacteria resistant to antibiotics?

[Amy Z]

The bacteria that have plasmids which code for some trait that enables them to be resistant will not die when subjected to antibiotics, but all of the other bacteria will.
Since the other bacteria are all dead, only the resistant bacteria will be able to replicate and create new bacteria, which will also be resistant.

Also, the bacteria already have to the resistant gene. Subjecting them to antibiotics would not cause them to be resistant (this is a common misconception some people have).

Therefore, the bacteria that are resistant are naturally selected for against the ones that aren't.

If someone argues that this isn't 'natural' selection, keep in mind we get many of our antibiotics from our environment. Many fungi produce antibiotics (like penicillin) that would help select for resistant bacteria in that environment.