Aerobic and anaerobic microbiology of periapical abscess.

Aspirates of pus from periapical abscesses in 39 patients were studied for aerobic and anaerobic bacteria. Bacterial growth was present in 32 specimens. A total of 78 bacterial isolates (55 anaerobic and 23 aerobic and facultative) were recovered, accounting for 2.4 isolates per specimen (1.7 anaerobic and 0.7 aerobic and facultatives). Anaerobic bacteria only were present in 16 (50%) patients, aerobic and facultatives in 2 (6%), and mixed aerobic and anaerobic flora in 14 (44%). The predominant isolates were Bacteroides spp. (23 isolates, including 13 Bacteroides melaninogenicus group), Streptococcus spp. (20), anaerobic cocci (18), and Fusobacterium spp. (9). Beta-lactamase-producing organisms were recovered from 7 of the 21 (33%) specimens that were tested. This study highlights the polymicrobial nature and importance of anaerobic bacteria in periapical abscess.