Antimicrobial activity of antibiotic pastes used in pulp therapy through direct contact with a multispecies biofilm: a pilot study

Objective: To evaluate the antimicrobial activity of antibiotic pastes used in lesion sterilization and tissue repair (LSTR) technique, through a novel membrane direct contact methodology against a multispecies biofilm and to establish appropriate dilutions for this method. Methods: CTZ (chloramphenicol, tetracycline, zinc oxide) and two formulations of 3Mix pastes (ciprofloxacin, metronidazole, and minocycline), 3Mix1 and 3Mix3, were evaluated with negative (0.9% saline) and positive (chlorhexidine 0.2%) control groups. Candida albicans and Enterococcus faecalis (24-hour) biofilms (n=10) grown on cellulose membranes were directlyexposed to standardized amounts of fresh pastes and control solutions (n=2) for 24h. Membranes were immersed in 900 μl of saline solution, and seven serial dilutions were made for each sample. Plating for each dilution (n=2) was performed on culture media for microbial colony-forming unit (CFU) counting of totalmicroorganisms, Candida spp. and Enterococcus spp. Aiming the comparison between groups, CFU quantification data were transformed into log10 CFU / mL and the Mann-Whitney test was applied (p<0.05). Results: Inhibition of CFU was observed for all pastes, with greatest effects for CTZ paste in medium selective for Candida spp. (p<0.001) and 3Mix1 in non-selective (p<0.000) and selective for Enterococcus spp. (p<0.004). Conclusion: The pastes showed antimicrobial activity against the tested multispecies biofilm, and the proposed direct contact methodology was efficient. Moreover, the dilutions used proved to be appropriatefor this methodology.