Potential anti-biofilm effect of Centella asiatica against Porphyromonas gingivalis

Abstract

The oral cavity harbors several hundred coexisting microbial species, which are kept in check by the host immune system. Several oral diseases, such as periodontitis, peri-implantitis, and fungal infections, are caused by imbalances in microbial–microbial and microbial–host immunity. Bacteria exist in a planktonic or biofilm state. They grow and multiply faster when in a planktonic state but are more resistant to external harm when present in biofilm. Streptococcus mutans is important in biofilm formation and development. It contributes to biofilm mass formation, because of its glucan production, and is a useful organism for basic research on biofilm. Porphyromonas gingivalis is a pathogenic bacterium that causes periodontal disease. Its virulence factors, including lipopolysaccharide (LPS) and gingipain, the main cause of periodontal tissue inflammation and dysbiosis of the periodontium. The herbal medicine Centella asiatica has antimicrobial activity and anti-inflammatory effects and is used to treat periodontal disease. However, no study has investigated the effect of Centella against oral pathogens. The study was divided into two parts. First, basic biofilm formation and migration were studied in S. mutans biofilms on the surfaces of miniscrews and tooth roots. Second, the antibacterial activity, anti-biofilm effects, anti-gingipain activity, and anti-inflammatory effects of Centella extract against P. gingivalis were studied. Chapter 2 discusses the formation, migration, and morphology of biofilms on different surfaces of the oral cavity, as these characteristics explain the differences in inflammatory progression between periodontitis and peri-implantitis. An S. mutans biofilm was used to represent biofilm formation on miniscrews and tooth roots. In addition, a modified flow system was created and used to supply nutrition and imitate the dynamic system of the oral cavity during biofilm formation. Although biofilm formation was faster on tooth root surfaces at 24 hours, migratory rates were faster on miniscrew surfaces at 48 hours. Morphology did not differ in relation to surface. A basic technique for studying biofilm formation was developed; however, a modified system could not be used in the subsequent study of P. gingivalis, as it was not possible to achieve completely anaerobic conditions. Chapter 3 describes the effect of a Centella asiatica aqueous extract against the periodontal pathogenic bacteria, P. gingivalis. The Centella extract exerted antibacterial activity at a concentration of 1 mg/ml or higher. At low concentrations, the extract inhibited biofilm development by means of a non-bactericidal mechanism. Gingipains, a virulence factor related to biofilm formation, was suppressed by the extract. In addition, the ability to reduce the inflammatory responses of periodontal ligament cells was confirmed. This study is a first step in understanding the effect (and especially the anti-biofilm effect) of Centella extract against oral pathogens. Biofilms are resistant to external harm; thus, agents that inhibit biofilm formation and suppress bacterial virulence factors are crucial in effectively treating oral disease.