Testanus is a soil-born organism. You're far more like to get infected by it when you graze your knuckles gardening than when being bitten by a mouse (or, indeed, by anything else).
People get bitten by dogs, cats, mice, ferrets, etc every day but we don't seem to hear about them contracting anything nasty from such bites. If the wound shows obvious signs of infection (such as feeling hot and tender) it will be time to seek out some antibiotics. Otherwise ignore it.