Rhamnolipids and surfactin inhibit the growth or formation of oral bacterial biofilm
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RESEARCH ARTICLE
Open Access
Rhamnolipids and surfactin inhibit the growth or formation of oral bacterial biofilm Ryota Yamasaki* , Aki Kawano, Yoshie Yoshioka and Wataru Ariyoshi
Abstract Background: Bacteria survive in various environments by forming biofilms. Bacterial biofilms often cause significant problems to medical instruments and industrial processes. Techniques to inhibit biofilm formation are essential and have wide applications. In this study, we evaluated the ability of two types of biosurfactants (rhamnolipids and surfactin) to inhibit growth and biofilm formation ability of oral pathogenic bacteria such as Aggregatibacter actinomycetemcomitans, Streptococcus mutans, and Streptococcus sanguinis. Results: Rhamnolipids inhibited the growth and biofilm formation ability of all examined oral bacteria. Surfactin showed effective inhibition against S. sanguinis ATCC10556, but lower effects toward A. actinomycetemcomitans Y4 and S. mutans UA159. To corroborate these results, biofilms were observed by scanning electron microscopy (SEM) and confocal microscopy. The observations were largely in concordance with the biofilm assay results. We also attempted to determine the step in the biofilm formation process that was inhibited by biosurfactants. The results clearly demonstrated that rhamnolipids inhibit biofilm formation after the initiation process, however, they do not affect attachment or maturation. Conclusions: Rhamnolipids inhibit oral bacterial growth and biofilm formation by A. actinomycetemcomitans Y4, and may serve as novel oral drug against localized invasive periodontitis. Keywords: Biofilm inhibition, Oral bacteria, Rhamnolipids, Surfactin
Background Biofilms are three-dimensional structures consisting of various microbial populations attached to a surface by extracellular polymeric substances (EPS) produced by these microorganisms [1]. Bacteria are physically shielded from external stresses by this extracellular matrix, [2]. Although biofilms can be beneficial in industrial processes such as wastewater treatment [3], fermentation [4], and microbial fuel cells [5, 6], they can also cause harmful effects, including biocorrosion by sulfate-reducing bacteria [7], infection due to biofilm formation on medical devices, * Correspondence: [email protected] Division of Infections and Molecular Biology, Department of Health Promotion, Kyushu Dental University, Kitakyushu, Fukuoka 803-8580, Japan
such as catheters, pacemakers, and artificial joints [8], and oral diseases such as tooth decay and periodontal disease [9]. Streptococcus mutans, a representative bacteria of tooth decay [10], forms plaques (biofilm) on tooth surfaces and produces lactate from sugars such as sucrose, which demineralizes teeth and causes dental caries. Streptococcus sanguinis is another plaque-forming strain that has been reported to cause infective endocarditis by forming biofilms on the endocardium and heart valves [11]. Aggregatibacter actinomycetemcomitans has been strongly associated with localized aggressive
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