[js1138]

Not necessarily. Firstly, we don't know if these are replication errors, or are a response to environmental stimulii that are within the bacteria's genetic coding.

I don't believe this. For example, if mutation is a "designed" response to antibiotics, then the mutation rate would be very high in the presense of an antibiotic. After all, a given colony of bacteria is composed of nearily identical clones.

But the rate doesn't change. all that happens is that survivors increase in numbers because they are the only ones left standing.

[Frumious Bandersnatch]

I don't believe this. For example, if mutation is a "designed" response to antibiotics, then the mutation rate would be very high in the presense of an antibiotic. After all, a given colony of bacteria is composed of nearily identical clones.

The mutation rate wouldn't necessarily be very high.  There are many other factors involved (such as the amount of outside stimulii received).  As far as "nearly identical" is concerned, they are still separate and distinct organisms and are not nearly identical as we would first think.

But the rate doesn't change. all that happens is that survivors increase in numbers because they are the only ones left standing.

If a bacterium gets a less than life-threatening dose of poison, what's so unreasonable about the fact that it develops a further immunity against said poison?  This is not mutation.  The same bacterium after a period of time can lose said immunity.