Only buy white bath towels. Add bleach to the prewash and use vinegar instead of fabric softener.
I instituted this practice several years ago and it works like a charm.
A few rules to I live by:
1) Vinegar and bleach will kill any and every germ they encounter. They are twice as powerful together. These two substances can replace just about every other household cleaning product - they are far more effective and don't leave any harful residue behind. AND, bonus vinegar helps colorfast your brights.
Remember to be smart - don't use bleach (or mix bleach and vinegar) in a confined space where you would breathe them in.
2) Liquid fabric softener promotes mildew growth - you know that funky smell your laundry can take on when you forget to change the load overnight? Yep. That's mildew. White vinegar works better than Downy - I SWEAR TO YOU IT'S TRUE.
3) Front loading washing machines are water (and air) tight. Duh. Mildew loves a dewey, air-tight space to grow. So always leave the door open between cycles. If your machine does get funk-i-fied, then a cycle with bleach and vinegar will help flush it out.