This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Periapical granuloma is 
Select and explain. 
A. Anaerobic infection, B. Aerobic infection, C. Mixed infection, D. Sterile
D: Sterile
Answer: D: Sterile 
Explanation: A direct lift from Cohen.
Bacteriological features of periapical granuloma:

Majority of the studies have been based upon bacteriological cultures taken after the extraction of tooth
Pre extraction cultures have been made in a few instances through the root canal or the alveolar plate and these have been relatively free of actual contamination.
The microorganisms that have been isolated by such techniques were, generally found in oral cavity such as  s.viridans, s.albus, e.coli and pneumococci.
Seldom can microorganisms actually be demonstrated histologically in the periapical granuloma.
 Some investigators have suggested that dental granuloma is usually a sterile lesion.