Optimization and Genetic study on Locally Isolated Streptococcus mutans for Mutacin Production

     In order to isolate Streptococcus mutans, 80 swab samples were collected from dental caries of patients attended Al-Dora Health Center and Al-Zewiya Health Center in Baghdad city. From these samples, 98 bacterial isolates were obtained. Results of  identification depending on morphological, cultural and biochemical tests showed that 10 of these isolates were belonged to Streptococcus mutans. The results of identification were confirmed by using VITEK-Π system. All isolates were screened to examine their ability to mutacin production. Results showed that all isolates were mutacin producers with variable degrees depending on mutacin inhibitory effect produced in the culture filtrates of these isolates against the test microorganism (Streptococcus pyogenes). S. mutans S2 which gave a highest inhibition zone (20mm) against S.pyogenes was selected for further studies. The optimum conditions for mutacin production was supplemented  the production medium (brainheart infusion broth) with 3% sucrose (as a sole source for carbon and energy) , 2% yeast extract (as a nitrogen source) and 0.5% KH  (as a PO phosphate source), with an intial medium pH of 6, in addition to incubation at 37°C for 24 hours under anaerobic conditions. Under these conditions the maximum mutacin production by S. mutans S2 against S. pyogenes was reached 35mm in diameter.   When antibiotic susceptibility of S. mutans S2 was examined against different antibiotics, results showed that this isolate was resist to bacitracin and erythromycin, while sensitive to amoxicillin, ampicillin chloramphenicol, vancomycin, clindamycin, impenem, gentamicin and cephalothin.
     Plasmid content of S. mutans S2 was studied to investigate its role in mutacin production by extraction of plasmid DNA, then electrophoresis on agarose gel. Results showed this isolate had one  plasmid DNA band, but not responsible for antibiotic resistance and for mutacin production according to the obtained results of curing by using interchalating ethidium bromide dye in a concentration of 800 μg/ml. adversely, cured cells were still having  ability of mutacin production which indicats that this trait may be is a chromosomally encoded.