Good Bugs vs Bad Bugs: Evaluation of Inhibitory Effect of Selected Probiotics against Enterococcus faecalis

The main goal of endodontics is the prevention of apical periodontitis. This is due to the presence of persistent pathogenic microorganisms, such as Enterococcus faecalis, and its ability to directly cause acute and chronic inflammation in the periapical tissues. Lactobacillus has been shown to promote health in the intestines as well as to inhibit the growth of certain problematic oral bacteria. This study explores shifting the established paradigm of endodontic treatment, which has focused on eliminating all bacteria from the canal system and on elimination of the problematic bacteria through introducing probiotics. A preliminary work was performed to evaluate the possible effectiveness of probiotics in preventing the growth of E. faecalis.

Two probiotic cultures Lactobacillus plantarum ATCC 8041 and Lactobacillus rhamnosus ATCC 7408 were selected to check their antimicrobial activity against E. faecalis ATCC 29212 by two methods: agar cup/well diffusion method and deferred antagonism test. Agar cup method: A total of 0.5 mL of requisite test pathogen culture was inoculated into 20 mL of molten sterile Mueller and Hinton agar and cooled to 45 ± 2°C. Circular wells of diameter 10 mm were punched in each of the poured plates. Appropriately diluted test samples were added to the above-punched wells. The plates were incubated upright position at 37°C for 24 hours in aerobic conditions. Postincubation, zone of inhibition was measured. The cell-free supernatant of Lactobacillus species was also evaluated for antimicrobial activity. Deferred antagonism test: The test probiotic strain was standardized to 0.1 optical density (OD) at 600 nm and inoculated in a 1 cm wide diametric streak across the surface of trypticase soy agar + yeast extract + calcium carbonate (TSYCa) agar using a sterile cotton swab. Then, the plate agar containing the test strain was incubated at 37°C for 24 hours under aero-philic condition and then standardized to 0.1 OD at 600 nm for overnight (18 hours, 37°C). A purified culture of indicator strain (pathogen) was streaked at right angles to the line of original producer growth. Postincubation plates were observed for the inhibition zone width of the indicator strain.

Under the conditions of this study, Lactobacilli had an inhibitory effect on the growth of E. faecalis by agar cup method but not by deferred antagonism test.

This pilot study demonstrated that probiotics show a potential in root canal therapy.

If probioitcs are effective against end-odontic pathogens, they can be potentially used as intracanal medicaments. This will be a novel concept of introducing bac-teriotherapy in endodontics and replacing pathogenic bacteria by healthy bacteria, normal flora.