Abstract
Oral streptococci are primary colonizers of tooth surfaces and Streptococcus mutans is the principal causative agent of dental caries in humans. A number of proteins are involved in the formation of monospecies biofilms by S. mutans. This study analyzed the protein expression profiles of S. mutans biofilms formed in the presence or absence of S. gordonii, a pioneer colonizer of the tooth surface, by two-dimensional gel electrophoresis (2-DE). After identifying S. mutans proteins by Mass spectrometric analysis, their expression in the presence of S. gordonii was analyzed. S. mutans was inoculated with or without S. gordonii DL1. The two species were compartmentalized using 0.2-μl Anopore membranes. The biofilms on polystyrene plates were harvested, and the solubilized proteins were separated by 2-DE. When S. mutans biofilms were formed in the presence of S. gordonii, the peroxide resistance protein Dpr of the former showed 4.3-fold increased expression compared to biofilms that developed in the absence of the pioneer colonizer. In addition, we performed a competition assay using S. mutans antioxidant protein mutants together with S. gordonii and other initial colonizers. Growth of the dpr-knockout S. mutans mutant was significantly inhibited by S. gordonii, as well as by S. sanguinis. Furthermore, a cell viability assay revealed that the viability of the dpr-defective mutant was significantly attenuated compared to the wild-type strain when co-cultured with S. gordonii. Therefore, these results suggest that Dpr might be one of the essential proteins for S. mutans survival on teeth in the presence of early colonizing oral streptococci.
Highlights
The development of dental caries is a complex process which is dependent on a presence of microbial biofilm known as dental plaque [1]
The tooth surface is colonized by a group of bacteria called “pioneer colonizers,” which are mostly composed of mitis group streptococci (e.g., S. gordonii, S. sanguinis, and S. mitis)
Colonizers such as S. mutans subsequently adhere to these pioneer colonizers [3, 4]
Summary
The development of dental caries is a complex process which is dependent on a presence of microbial biofilm known as dental plaque [1]. S. mutans Competition in Initial Attachment to Teeth biofilm, Streptococcus mutans has been considered as the bacterial species most closely associated with initiation of human dental caries [2]. Oral bacteria form a biofilm on the tooth surface that accumulates through the sequential and ordered colonization of more than 500 different species of bacteria [2]. Initial colonizers bind to host-derived receptors on the salivary pellicle of the tooth enamel. Of these bacteria, the oral commensals S. gordonii and S. sanguinis are representative pioneer colonizers of the pellicle [5, 6]. Clinical studies have indicated that S. sanguinis and S. gordonii can antagonize S. mutans colonization when present in oral biofilms in high numbers [10]
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