Microbiological and environmental assessment of human oral dental plaque isolates

Abstract Plaque-related diseases are amongst the most common ailments of the oral cavity. Streptococcus mutans is the causal agent of dental caries in animals and humans and is responsible for the formation and accumulation of plaques. This study aimed to identify and evaluate the role of the dental plaque isolates and its surrounding environment in plaque formation or inhibition. The study started with the identification of human dental plaque isolates from high caries index patients based on 16S rRNA and Mitis salivarius bacitracin agar (MSB) was used for  S. mutans  growing. Unexpectedly, the Streptococcus mutans was completely absent. The disc diffusion assay recorded that all the isolates had antimicrobial activity against the S. mutans growth. Enzymes assay revealed that the isolates produced dextransucrase, levansucrase and levanase activity with wide variation degrees. Also, the lactic acid production assay was done based in pH shift assessment. The highest pH shift and dextran yield were detected by the isolates Bacillus subtilis _AG1 and Bacillus mojavensis_ AG3. The adherence test revealed that Lysinibacillus cresolivorans _W2 (MK411028) recorded the highest adhesion property (60%). Oligo- and polysaccharides were synthesized by the action of dextransucrase enzyme and their cytotoxicity tests were negative. Dextran with a molecular weight (117521 Da) recorded the highest antimicrobial efficacy against Bacillus subtilis _AG1 and Bacillus mojavensis_ AG3 (65%, 63.5%) respectively. The results concluded that the dextran was the most important factor causing the dental plaque pathogenicity. Also, oral oligo- and polysaccharides might play a role in dental plaque control.