Why are bacteria vulnerable to high mutation rates?

Bacteria may seem to mutate at high rates because their replication cycles can be very short. Under optimal conditions an E. coli can duplicate within 20 minutes. That is even faster than it takes to duplicate it's genome. They use a trick to achieve that, i.e. starting the next replication before the first is completed. read more

The mutation rate per nucleotide may not be higher in bacteria, but they continuously put mutations to the test of viability (every 20 minutes, under optimal conditions), whereas in our case it is once every human generation. read more

From my reading on M. tuberculosis, I know that this organism has a pretty high mutation rate. Huh, that's news to me. In fact, Mtb has a rather low mutation rate and rather low genetic variance. See the paper by Sherman & Gagneux in Nature genetics. read more

Bacteria, and many other viruses (smallpox, herpes) have mutation rates that are similar to humans, so this is not a universal thing. The frequency of harmful mutations in viruses and bacteria is broadly about the same as you'd see in humans, though it's hard to do a one to one comparison. read more