ent-Copalic acid antibacterial and anti-biofilm properties against Actinomyces naeslundii and Peptostreptococcus anaerobius

Diterpenes are an important class of plant metabolites that can be used in the search for new antibacterial agents. ent-Copalic acid (CA), the major diterpene in Copaifera species exudates, displays several pharmacological properties. This study evaluates the CA antibacterial potential against the anaerobic bacteria Peptostreptococcus anaerobius and Actinomyces naeslundii. Antimicrobial assays included time-kill and biofilm inhibition and eradication assays. Time-kill assays conducted for CA concentrations between 6.25 and 12.5 μg/mL evidenced bactericidal activity within 72 h. CA combined with chlorhexidine dihydrochloride (CHD) exhibited bactericidal action against P. anaerobius within 6 h of incubation. As for A. naeslundii, the same combination reduced the number of microorganisms by over 3 log10 at 24 h and exerted a bactericidal effect at 48 h of incubation. CA at 500 and 2000 μg/mL inhibited P. anaerobius and A. naeslundii biofilm formation by at least 50%, respectively. CA at 62.5 and 1.000 μg/mL eradicated 99.9% of pre-formed P. anaerobius and A. naeslundii biofilms, respectively. These results indicated that CA presents in vitro antibacterial activity and is a potential biofilm inhibitory agent. This diterpene may play an important role in the search for novel sources of agents that can act against anaerobic bacteria.