Heliopsis longipes, a mexican endemic plant known as chilcuague, has been used in ethnomedicine as a salivation stimulant, anesthetic, and in treating throat infections and oral diseases. However, its activity on bacteria in the oral cavity has yet to be fully documented. This study evaluated the antibacterial activity of an ethanolic extract of HH. longipes (EEHLEEHL) roots on cariogenic strains (StreptococcusStreptococcus mutans and LactobacillusLactobacillus acidophilus).

EEHL was obtained by macerating 100 g of dried and ground plant material in 96° ethanol (1:10). Agar well diffusion technique was used, the inoculum was 100 µL (1x106 CFU/ml) of Streptococcus mutans (ATCC 25175) on BHI plates and Lactobacillus acidophilus (ATCC 314) on MRS plates in 5% CO2 atmosphere at 37ºC for 72 h. To determine the minimum inhibitory concentration (MIC), seven dilutions of an affinin standard at 320, 240, 160, 80, 40, 20, and 10 μg/mL were prepared in 12.5% EtOH and seven dilutions of EEHL (equivalent to the same affinin concentrations) in 3 vehicles: a) 12.5% EtOH (A); b) a mixture (C) of Labrasol® + Transcutol® + propylene glycol + Tween® 80; and c) a mixture (F) of excipients without Labrasol®. A 0.9% saline solution was used as a negative control. Chlorhexidine at 0.12% was used as positive control; vehicle and excipient effects were evaluated. The antibacterial activity was based on the halo measurement (mm).

Antibacterial activity of EEHL was observed against S. mutans and L. acidophilus at 240 and 160 μg /mL. These results were contrasted with the effect of the affinin standard (MIC = 240 μg/mL). Furthermore, substantial inhibition halos were observed for formulations C and F, suggesting a synergistic effect between EEHL and the excipients, specifically Labrasol®, which showed an inhibition effect on bacterial growth. However, this has not been reported as an antimicrobial agent.