I'm happy, and somewhat embarrassed, to admit that I already adhere to the once a month rule. Jeans are at their peak comfort after at least five wears. They are actually pretty uncomfortable after a fresh wash imo. That said, I've never washed any of my clothes because I was concerned with bacteria, usually it has more to do with some mustard stain, or a bit of funk emanating from the armpits or "nether-regions."
But a dirty pair of jeans is a comfortable pair of jeans.