Potential application of two tectivirus and cystovirus isolated from the Caspian Sea for bio-control of dental plaque using in vitro assay

The aggregation of oral Streptococci results in the beginning of enamel calcium degradation of the teeth and subsequent emergence of dental caries. Bacteriophages have a considerable effect in controlling the populations of various bacteria. The isolation and characterization of specific lytic bacteriophages against oral streptococci were the main goals of this study. Brain Heart Infusion Broth (BHI) culture medium was used for oral streptococci enrichment from dental plaque. The Mitis Salivarius Agar (MSA) culture medium was applied to oral streptococci isolated from dental plaque samples. A 0.45 μm membrane filtrate of Caspian Sea water was added to the streptococcal isolate suspension and cultured using the overlay method. The isolated bacterium on MSA, according to macroscopic, microscopic and biochemical examinations, was identified as Streptococcus salivarius. The BLASTN of the gtfK gene after DNA sequencing reconfirmed that the isolate was S. salivarius. The strain was named S. salivarius KBM-ISF-2 and its gtfK gene deposited at the GenBank, National Center for Biotechnology Information, NCBI, under the accession number KJ634208.1. Transmission electron microscopy revealed two specific lytic bacteriophages that attacked S. salivarius KBM-ISF-2 isolated from dental plaques. The first lytic phage was identified as a Tectivirus with icosahedral symmetry measuring 46.67 nm in diameter. The second phage was identified as a Cystovirus with icosahedral symmetry and a diameter of 85.56 nm. This is the first report of isolation and characterization of a Tectivirus from the Caspian Sea and its specific inhibiting effects on S. salivarius KBM-ISF-2. Also, a Cystovirus against S. salivarius KBM-ISF-2 was isolated and identified.