Infection of the mastoid, often follows otitis media.
If > age 2 you have a mastoid; often follows URI's.
Chronic: S. aureus and gram-negative enteric bacilli.
Atypical mycobacteria are not uncommon, presenting with refractory otorrhea and lots of granulation tissue and are best treated with surgery (PubMed)
In other words; damn near anything will work.
Chronic: it is best to let cultures be you guide; treating empirically is path down which lies madness.
Occasionally will be the source of a cerebellar abscess.
Relevant links to my Medscape blog