Explain to me what a "favorable mutation" is.
Here's a couple more facts.
1. The average bacterium has, say 3000 genes. If you have 1,000,000 mutants in your flask, most of those genes were hit more than once. There are some parts of the genome where mutations occur at very high frequencies, and some other areas where the frequencies are considerably lower.
2. A mutation is a change in the DNA sequence. Most mutations have no visible effect on the bacterium. A few mutations will be lethal, but you won't see those under normal circumstances, the bug just dies. The rest are "neutral" or "beneficial" or "not beneficial", but not lethal, etc.. See why I need to know what you mean by "favorable"?
As a layman, I'd say one that adds information to the genome but like I said, I'm a layman. :-}