Abstract
BackgroundBacteria 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.ResultsRhamnolipids 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.ConclusionsRhamnolipids inhibit oral bacterial growth and biofilm formation by A. actinomycetemcomitans Y4, and may serve as novel oral drug against localized invasive periodontitis.
Highlights
Bacteria survive in various environments by forming biofilms
The results showed that rhamnolipids significantly inhibited the growth of S. mutans UA159 and S. sanguinis ATCC10556, A. actinomycetemcomitans Y4 was not affected (Fig. 1a-c)
Rhamnolipids completely inhibited the growth of A. actinomycetemcomitans Y4 at a concentration of 3.25 w/v% (Fig. 1a)
Summary
Rhamnolipids and surfactin exhibit variable inhibitory effects on bacterial cell growth First, the ability of rhamnolipids and surfactin to inhibit the growth of bacteria was investigated. Treatment of S. mutans UA159 with surfactin promoted biofilm formation with no inhibitory effect observed at any concentration (Fig. 2e). Concentrations > 2.53 × 10− 3 w/v% of surfactin caused near complete inhibition of S. sanguinis ATCC10556 biofilm formation (Fig. 2f). We observed that pre-treatment with > 0.81 w/v% rhamnolipids effectively inhibited more than 63% of A. actinomycetemcomitans Y4 biofilm formation (Fig. 4b left), thereby confirming its inhibitory effect on the attachment process. The primary effect exhibited by rhamnolipids does not appear to be associated with the maturation process Taken together, these results indicate that the inhibitory effect of biosurfactants, rhamnolipids, toward the formation of biofilms by oral pathogenic bacteria, targets a stage after attachment, from initiation to maturation. Clinical studies on healthy subjects or patients with localized invasive periodontitis caused by A. actinomycetemcomitans Y4 are warranted to validate biosurfactants as a medicine for periodontal disease
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