Optimum Conditions for Mutacin Production From Streptococcus mutans S2

Mutacin production by Streptococcus mutans S2 was detected by inoculating production medium (Brain Heart Infusion broth supplemented with yeast extract 2% (w/v) and CaCO3 1% (w/v)) with fresh culture of the bacterial isolate. The inhibitory effect of mutacin produced by S. mutans S2 was studied by detection the inhibitory effect of mutacin against the test microorganism (Streptococcus pyogenes) grown on BHI agar plates. Optimum conditions for mutacin production from S. mutans S2 includes optimum carbon, nitrogen and phosphate sources and their concentrations, optimum temperature and pH. were studied. Results showed that these conditions include the supplementation of the production medium (Brain-Heart Infusion broth containing 1%CaCO3) with sucrose as a sole source for carbon and energy at a concentration of 3%, and yeast extract as a nitrogen source at a concentration of 2%, and KH2PO4 as a phosphate source at a concentration of 0.5%, with initial medium pH of 7, then inoculating with fresh culture (OD 0.8), and incubation at 37°C for 24 hours in candle jar. Under these conditions the maximum mutacin production S. mutans S2, causing maximum inhibition effect against test microorganism (S. pyogenes) reached 35 mm in diameter. Introduction The increase of microbial resistance to antibiotics has led to a continuing search for newer and more effective drugs (1). Antimicrobial peptides present new possibility for combating infectious diseases. They inhibit the growth of pathogenic microorganisms, without affecting the host or the animals and plants that produce them, and have a broad spectrum antimicrobial activity. It is well known that bacteria, induced by stress, produce bacteriocins which is promising antimicrobial substances that may cure infectious diseases (2). Bacteriocins are found in almost every bacterial species examined to date, and within a species tens or even hundreds of different kinds of bacteriocins are present (3). Mutacin as bacteriocins are proteinaceous antibacterial substances produced by Streptococcus mutans (4). S. mutans is a Gram-positive bacterium, which plays a key role in the formation of the dental plaque biofilm as an early coloniser (it produces adhesions which attach the organism to the acquired pellicle of the teeth) and is the most important bacterium in the formation of dental caries. S. mutans classified into four serotype (c, e, f, k) based on chemical composition of its cell surface serotype specific rhamnose-glucose polymers (RGPs), which form backbone of rhamnose polymer with side chain of glucose polymers (5). Bacteriocins produced by the oral bacterium Streptococcus mutans are divided into two groups: (i) the lanthionine-containing (lantibiotic) mutacins and (ii) the unmodified mutacins. While most bacteriocin activities characterized to date consist of a single active polypeptide, several two-component lantibiotic and nonlantibiotic bacteriocins have also been described, and these are depend upon the collaborative activity of two polypeptides to exert their full antimicrobial activity(6). The lantibiotics are small peptides containing lantionina, β-methyl-lantionina dehidratados residues and are synthesized by ribosomes and are modified after translation (7). This study was achieved to produce mutacin from S. mutans under optimum conditions. Materials and Methods Bacterial isolate Bacterial isolate identified as S. mutans S2 was obtained from dental caries sample (8). This isolate was maintained on Brain Heart Infusion agar medium.