Microbial diseases of the oral cavity are among the most common infectious diseases of humans [1]. However, conventional preventive and curative chemical dental care is often related with limited efficacy and unwanted side effects of oral antiseptic agents [2]. Although plants are considered as perspective sources of novel compounds with antimicrobial properties [3], little is still known about their effectiveness against oral pathogenic organisms [4].
The objective of this research was to investigate in vitro growth-inhibitory effect of 109 plant species (including eight hop varieties) from Generally Recognized as Safe (GRAS) list against oral pathogenic microorganisms. Two-fold dilution of ethanol (all species) and supercritical fluid extracts (hop varieties only) with concentration range from 512 to 1 µg/mL were tested against Aggregatibacter actinomycetemcomitans, Bifidobacterium dentium, B. longum, Candida albicans, Eikenella corrodens, Fusobacterium nucleatum subsp. vincentii, Lactobacillus salivarius, Porphyromonas gingivalis, Streptococcus mutans, S. salivarius and S. sobrinus using the broth microdilution method in anaerobic conditions (except of C. albicans) [5, 6].
The best results were obtained for Humulus lupulus, whereas supercritical extract obtained from variety Herkules was found to produce the strongest antimicrobial effect with MIC values ranging from 8 to 512 µg/mL. It was found that Helichrysum angustifolium showed good antimicrobial potential against S. mutans and S. salivarius and Myristica fragrans against F. nucleatum subsp. vincentii with the MIC 64 µg/mL. Xanthoxylum clava-herculis had the antimicrobial activity of MIC 64 µg/mL and 128 µg/mL for S. sobrinus and S. salivarius respectively.
Even though there were some previous studies evaluating the antimicrobial potential of individual plant species from the GRAS list [e.g. 7, 8], this is the first complex study monitoring their antimicrobial activity against main oral pathogens. Our results suggest that the extracts of H. lupulus (particularly of certain varieties) have potential as new safe antimicrobial agents that can be incorporated in oral herbal care products.