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Background and Objective: Probiotics' effects on harmful oral bacteria have been verifed. As antibiotic resistance becomes a major problem, searching for novel potential species is important. The objective of this study was to select novel safe strains of lactic acid bacteria with potentials as oral probiotics. Furthermore, ability of these strains to suppress growth and attachment of Streptococcus mutans as the most important cariogenic bacteria in tooth decay was investigated. Material and Methods: Initial identification tests, including Gram staining and catalase and oxidase tests, were carried out on 22 strains of lactic acid bacteria isolated from Iranian traditional dairy products. Safety of the strains was assessed using hemolysis test and antibiotic resistance assessment. Strains were then assessed for probiotic characteristics such inhibition of Streptococcus mutans growth, tolerance to lysozyme enzymes and ability of adhesion as well as ability of decreasing Streptococcus mutans adhesion. Selected strains were identified using16S rRNA molecular method. Results and Conclusion: Of all strains, four strains with the optimal probiotic characteristics were selected. These included one Lactobacillus brevis, one Lactobacillus casei and two Lactobacillus paraceasei. These four strains showed strong antimicrobial characteristics against Streptococcus mutans, were resistant to oral lysozyme enzymes and included high adhesion abilities to polystyrene wells. Furthermore, they decreased Streptococcus mutans attachment; thus, biofilm formation by this bacterium was prevented. These strains were recognized as safe strains since they were approved in assessments of antibiotic susceptibility and hemolytic activity. Therefore, these four strains are suggested as oral probiotics. Conflict of interest: The authors declare no conflict of interest.

Background and Objective: Lactobacillus plantarum is one of the probiotics species used in functional food products. These bacteria or their purified bacteriocins are used as biological preservatives in the food industry. The first step in production of an array of probiotic products is optimizing production in fermentors. This study aimed to examine factors affecting the in vitro growth optimization of Lactobacillus plantarum T5JQ301796.1 in a lab scale fermentor.Materials and Methods: Following 24 hours of anaerobic culture of the lactobacillus at 37°C, the pre-culture was ready and was inoculated to a 5 liter fermentor at 37°C and stirred at 40 rpm. Then factors affecting lactobacillus growth including carbon and nitrogen sources and pH were studied. The results were interpreted using response surface methodology (RSM), and optimal conditions for the equipment were determined.Results and Conclusion: For optimal growth of Lactobacillus plantarum T5JQ301796.1 in lab scale fermentor, the optimal conditions were 25.96 gl-1 of glucose, 1.82% of yeast extract, pH of 7.26, and stirring at 40 rpm at optimum temperature between 37-40°C. In this condition, maximum viable cell in the batch fermentation was 1.25×1010 CFU ml-1. Application of central composite design for the growth optimization of this bacterium led to maximum viable cells equal to 1.25×1010 CFU ml-1. So the mentioned features can lead to optimum industrial scale production and usage of this probiotic strain in probiotic products.Conflict of interest: The authors declare that there is no conflict of interest.