Anorectal abscess is an abscess adjacent to the anus. It arises from an infection at one of the Because of the increasing appearance of more exotic bacteria in anal abscesses, microbiological examination will always be performed on the. The anus is an opening at the opposite end of an animal's digestive tract from the mouth. For details specific to the human anus, see Human anus. remained in the digestive tract; and dead or excess gut bacteria and other endosymbionts.