The antibacterial activity of the compounds egonol (1) and homoegonol (2), of the crude ethanolic extract of Styrax pohlii (Styracaceae) aerial parts (EE), and of its n-hexane (HF), EtOAc (EF), n-BuOH (BF), and hydromethanolic (HMF) fractions was evaluated against the following microorganisms: Streptococcus pneumoniae (ATCC 6305), S. pyogenes (ATCC 19615), Haemophilus influenzae (ATCC 10211), Pseudomonas aeruginosa (ATCC 27853), and Klebsiella pneumoniae (ATCC 10031). The broth microdilution method was used for determination of the minimum inhibitory concentration (MIC) during preliminary evaluation of antibacterial activity. The EE yielded MIC values of 400 µg/mL for S. pneumoniae and P. aeruginosa and 300 µg/mL for H. influenzae. The HF and EF fractions exhibited enhanced antibacterial activity, with MIC values of 200 µg/mL against S. pneumoniae, but only EF displayed activity against H. influenzae (MIC 200 µg/mL). The best MIC value with compounds 1 and 2 (400 µg/mL) was obtained for (1) against S. pneumoniae and P. aeruginosa. Therefore, 1 exhibited weak antibacterial activity against these standard strains.

Viguiera arenaria, family Asteraceae, is a plant that contains diterpenoids, which make this species potentially applicable in endodontics. More specifically, V. arenaria contains diterpenes of the pimarane type, which display various classic biological activities. This study evaluates the antibiofilm activity, the time-kill curve, and the inhibitory concentration index of diterpenes of the pimarane type (entpimara-8(14),15-dien-19-oic acid, ent-8(14),15-pimaradien-3β-ol, and ent-8(14),15-pimaradien-3β-19-oic acid sodium salt, designated diterpenes I, II, and III, respectively) toward nine anaerobic bacteria commonly found in endodontic infections; this study also assesses the cytotoxic activity of these diterpenes against human fibroblasts. According to the antibiofilm assay, diterpenes I, II, and III inhibit at least 50% of all the bacteria. On the basis of the time-kill curve experiments, the behavior of these diterpenes depends on the tested bacteria, diterpene concentration, and microorganism sensitivity. Synergism of diterpenes I and II with chlorhexidine (CDH) was higher against P. gingivalis (clinical isolate) and Aggregatibacter actinomycetemcomitans (ATCC). As for diterpene III, synergism with CDH is higher against P. micros. As revealed by the XTT assay, none of the diterpenes of the pimarane type tested here are cytotoxic. Hence, diterpenes I, II, and III are promising biomolecules and may provide therapeutic solutions in the field of endodontics.