Baizatul Amirah , Che Baharuddin (2018) Antimicrobial activity of Averrhoa Bilimbi fruit extract on simulated oral biofilm / Baizatul Amirah Che Baharuddin. Masters thesis, University of Malaya.
Abstract
This study was conducted to search for new active compounds from plant extracts that can be used as agents for plaque control. Streptococci dominate more than 600 bacterial species reported found in the dental plaque. At the initial phase of plaque or biofilm formation, the bacterial component colonising the tooth surface consisted mainly of the Gram-positive facultatives but as the biofilm becomes complex and matured, it shifts to consist of more Gram-negative anaerobes. While both Streptococcus sanguinis and Streptococcus mitis dominates the early phase of plaque formation, Streptococcus mutans tends to increase in population when the plaque has become more matured. This study was carried out to investigate the susceptibility of dental plaque bacteria that includes S. sanguinis, S. mitis and S. mutans to the extract of five plants: Averrhoa bilimbi, Brucea javanica, Euphorbia tirucalli, Nigella sativa and Vernonia amygdalina. The screening test was carried out at four different amounts (5, 10, 15 and 20 mg) using the disc diffusion method while the minimum inhibitory concentration (MIC) was determined using the microdilution assay. 0.12% (w/v) of chlorhexidine gluconate (CHX) and sterile distilled water were used as the positive and negative controls, respectively. It was found that all three bacteria were susceptible to the aqueous extract of A.bilimbi and V.amygdalina. The MIC of A.bilimbi was 6.25 mg/mL for all three Streptococcus sp. while V. amygdalina exhibited weak antibacterial response. Based on this screening, only the extract of A. bilimbi was selected for futher tests. It was determined that A. bilimbi has a minimum bactericidal concentration of 12.5 mg/mL for S. mutans dan S. mitis, and 25.0 mg/mL for S. sanguinis. Three active compounds of A. bilimbi were identified as ascorbic acid, acetylvitisin B and chinic acid. A. bilimbi also demonstrated slight aggregative effect. At a minimal concentration of 6.25 mg/mL iii (MIC), A. bilimbi extract demonstrated antiadhesion activity on the binding of bacteria to the acquired pellicle. Extract-treated pellicle was found to prevent bacteria adhesion and thus decreases bacteria population inside the biofilm by 64.5%. This extract also showed good antibacterial effect as it can decrease the hydrophobic properties of all three bacteria surfaces. Lost in hydrophobic properties is a negative effect to bacteria because it influences the bacteria adherence capacity during the early phase of biofilm formation. Exposure of biofilm-24hr to A. bilimbi for 30, 60 and 90 sec was found to be effective in reducing bacterial population in the biofilm by 24.1, 30.5 and 49.8%, respectively. At a minimal concentration of 6.25 mg/mL (MIC), A. bilimbi extract also exhibited antiadherence effect on the adhesion of bacteria to the acquired pellicle. Extract-treated pellicle showed antiadhesion activity by reducing the biofilm attachment to experimental pellicle by 64.5%. It also reduced the cell surface hydrophobicity of all streptococcus tested and make them less adherent. A. bilimbi also down regulated the expression of gtfB by almost 5-fold (RQ = 0.204), almost fully suppress gtfC (RQ = 0.008) and totally suppressed the expression of vicR gene (RQ = 0.000). The significant antibacterial properties exhibited by A. bilimbi extract suggested its potential use for plaque control.
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