The present study evaluated the microorganisms present in infected root canals. All teeth used in this study had primary root canal infections and had positive cultures in all the sixty teeth. Our study yielded negative cultures for the 10 control teeth which were selected for elective surgery (0% positive cultures). Total absence of positive cultures from control teeth, demonstrates the efficiency of the sampling technique used, and affirms the assertion by Shuping et al [9]that healthy vital pulps are largely free of microorganisms.
Some in vivo culture studies have demonstrated that primary endodontic infections are characterized by a mixture of organisms dominated by anaerobic bacteria and composed of a mean number of 2.6 to 5.4 species per canal.[10,11]In this study, at least two bacterial species were isolated per tooth with the highest number per tooth being 9. The average number of bacterial species per tooth was 4.85 ± 1.41 species.
The 53 bacterial species isolated, were predominantly facultative anaerobes 26 (49.1%), followed by obligate anaerobes 15 (28.3%.) and 12(22.6%) aerobes. The species were mainly gram positive 37,(69.8%). Out of the gram positive species 22 (59.5%) were cocci. This is consistent with the findings of Ercan et al.[12] who found predominantly facultative anaerobes (52.7%) and gram positive (67.8%) microorganisms in their study. Some studies however found obligate anaerobes to be predominant.[6,4,13]
Facultative anaerobes and aerobic bacteria isolated in this study were similar to those mentioned in Lee et al’s[14] study. The facultative anaerobes isolated included, Enterococcus faecalis, Corynebacterium amycolatum, Rothia,Actinomyces.
The aerobes identified included Neisseria spp. Escherichia coli, Pseudomonas stutzeri, Enterobacter kobei, E.cloecae which are Gram negative rods were also identified.
The number of bacterial species isolated in this study was largely consistent with the array of bacteria in the review by Narayanan et al [15] in which S mitis, S oralis and S.mutans belonging to the viridans groups are the most frequently isolated bacterial species. Additional bacteria recovered in this study, belonged to Prevotella, Actinomyces and Rothia species respectively. These findings however differ from those of [16] where S. gordonii and S oralis were predominant in teeth with apical periodontitis
Regarding correlation between bacteria and type of infection, this study found that, irreversible pulpitis had mainly streptococcus species and provetella species. This is consistent with bacteria implicated and isolated in primary root canal infections as reported by Narayanan et al[15]
Teeth with diagnoses of apical abscesses (both acute and chronic) had mainly facultative anaerobes isolated. The species isolated were mainly Streptococcus spp, Actinomyces naeslundii, and Prevotella oralis, a black pigmented Gram negative rod.
The ecology of the root canal system changes with time and at increasing depths. With increasing bacterial population there is a reduction in available nutrition, as well as a decrease in the available oxygen. This favours facultative and strict anaerobes and allows them to thrive, which most likely explains the findings in this study and others.
These findings compares with findings by Fowel et al.[17] which implicated facultative anaerobes belonging to the streptococcus viridans anginosus group in dental abscess. However some studies have isolated Staphylococcus aureus frequently from acute dental abscess, ranging from 0.7–15%.[18,19]
The species isolated in Chronic abscess in this study were Gram positive cocci (Streptococcus oralis, Streptococcus mitis,Streptococcus constellatus,Strep constellatus) Enterococcus faecalis (Gram positive rods)Actinomyces odonlyticus,Actinomyces meyeri(Gram negative rods)(Fusobacterium nucleatum, and Enterobacter cloacae).
Facultative anaerobes, such as the viridans group streptococci and the Streptococcus anginosus group, and strict anaerobes, especially anaerobic cocci, Prevotella sp and Fusobacterium species have been observed as the most common organisms isolated in dentoalveolar abscess.[19]They have been found in 10–87% of dentoalveolar abscesses. [20,21]