Microbiological and clinical data from 56 patients with endodontic inf
ections were evaluated. Samples were collected using autoclaved paper
points, Specimens were processed for isolation of aerobic and anaerobi
c bacteria, Antimicrobial sensitivity and resistance profiles of the r
ecovered isolates was also performed. Forty nine positive cultures (87
.5%) were obtained from the 56 consecutive necrotic root canal systems
which were sampled, A total of 69 aerobic bacteria and 21 anaerobic b
acteria were recovered. Aerobic bacteria were isolated from 35 patient
s (72%), anaerobic bacteria from 3 (6%) and mixed aerobic and anaerobi
c bacteria from 11 patients (22%). The most common aerobic isolate was
Klebsiella pneumoniae. The predominant anaerobic isolate was Bacterio
des species. One isolate was recovered from 25 patients (51%) whereas
in the remaining 24 patients (49%) more than 1 isolate were recovered.
These data illustrate the polymicrobial nature of endodontic infectio
ns in half the patients studied and the role of anaerobic bacteria in
a quarter of them.