Abstract
Extracts from eucalyptus leaves have been reported to show antibacterial activity against various oral bacteria and to inhibit glucosyltransferase activity of Streptococcus mutans and Streptococcus sobrinus. Although the antibacterial mechanism of the extracts against cariogenic bacteria has been examined in detail, little is known about the antibacterial effect of the extracts on periodontopathic bacteria. The purpose of this study was to investigate the antibacterial activity of eucalyptus leaf extracts on various periodontopathic bacteria and to evaluate the possibility of developing the extracts to periodontal diseasepreventive substances. In order to examine the antibacterial activity, various periodontopathic bacteria were cultured in media with or without various amounts of extracts from eucalyptus leaves at 35℃ anaerobically, and OD_<660nm> was measured for 48 h. Extracts from green tea were used as control. The growth of tested periodontopathic bacteria was inhibited by 250μg/ml eucalyptus leaf extracts, especially, the growth of Porphyromonas gingivalis was strongly inhibited by addition of 10 μg/ml eucalyptus leaf extracts. This strong inhibition was observed in three strains of P. gingivalis, namely, ATCC 33277, OMZ 314 and W 50, indicating that eucalyptus leaf extracts had strong growth-inhibitory effects against a wide range of P. gingivalis. Although green tea extracts have been reported to possess antibacterial activity for P. gingivalis, growthinhibitory effect was weaker than that of eucalyptus leaf extracts at the concentration of 10 μg/ml in this study. In order to determine the nature of the inhibition, some periodontopathic bacteria were cultured in media containing determined amounts of eucalyptus leaf extracts at 35℃ anaerobically. At determined periods, aliquots were removed and applied on blood-agar plates. After incubation for 3 days, colony-forming units (CFU)/ml were counted. For P. gingivalis strains, no considerable decrease of CFU/ml were observed by incubation with 100 μg/ml eucalyptus leaf extracts for 36 h, suggesting that the antibacterial activity of eucalyptus leaf extracts against P. gingivalis was bacteriostatic but not bactericidal. Similar results were obtained for P. intermedia ATCC 49046 and Fusobacterium nucleatum ATCC 23726. From these results, it is suggested that extracts from eucalyptus leaves may have bacteriostatic antibacterial activity against various periodontopathic bacteria, especially P. gingivalis. Considering the significant antibacterial activity against P. gingivalis, extracts from eucalyptus leaves may be useful for clinical application as preventive substances for periodontal disease.
