Introduction:

The antibacterial properties of Plantago major against oral microorganisms have not been widely studied.

Objective:

Identify the secondary metabolites present in an ethanolic extract of Plantago major and determine their antibacterial activity against Streptococcus mutans.

Methods:

The Plantago major ethanolic extract (EE) was prepared at concentrations of 25%, 50%, 75% and 100%. Six paper discs were loaded with 10 µl, 15 µl, 20 µl and 25 µl of each concentration, for a total 96 discs, which were then placed on Petri plates with brain heart agar inoculated with Streptococcus mutans. The positive control was 0.12% chlorhexidine. Six replicates were estimated for each concentration. The plates were incubated at 37ºC for 48 hours. Inhibition haloes were measured with a digital caliper. Statistical analysis was based on one-factor ANOVA testing followed by Tukey's post hoc test.

Results:

Chemical analysis of the Plantago major ethanolic extract identified the presence of terpenes, diterpenes, saponins, terpenoids and essential oils. The 25% and 50% concentrations did not display an antibacterial effect, whereas volumes above 20 µl of the 75% concentration and all 100% volumes were effective to inhibit Streptococcus mutans growth with inhibition haloes of 8.36 mm to 14.64 mm. 0.12% chlorhexidine inhibited Streptococcus mutans with inhibition haloes of 17.77 mm on average, presenting significant differences with all the concentrations of the Plantago major ethanolic extract (p < 0.05).

Conclusions:

The Plantago major ethanolic extract was found to contain terpene and saponin derivatives, and displayed antibacterial activity against Streptococcus mutans at volumes and concentrations above 20 µl / 75 %.

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