| Summary: | 碩士 === 國立臺北教育大學 === 自然科學教育學系碩士班 === 99 === Recent studies on lactic acid bacteria (LAB) have focused on dental health. Some of them have been proved effective and subjected to commercially production. We have collected various fermented foods from different regions of Taiwan. 8 samples at the final stage of fermentation were used to isolate LAB. The technologies of microbial enumeration and isolation, grams stain and catalace activity assay, DNA extraction, RAPD-PCR, 16s PCR and DNA sequencing and blast were referred to identify LAB species. 135 strains of LAB were selected as the experimental group. Streptococcus mutans and Staphylococcus aureus were considered as the control groups for selection of antimicrobial abilities on LAB since they are supposed to cause dental caries and be harmful for oral health. Through observation of the inhibition zone, 50 LAB strains were suggested to inhibit the growth of S.mutans and Staphyl. aureus. 12 LAB were further verified to inhibit growth of S.mutans and Staphyl.aureus. to less than 20% when compared to those without LAB. After measurements of acid production, 10 LAB strains were believed suitable for application for oral health due to little pH variation during incubation in oral mimicked environment. When hydroxyapatite (HAP) was used to monitor the tooth enamel, 4 LAB strains were proved to have little effects on degrading (HAP), which effects were even superior than that of L. salivarius which was
thought to be beneficial for oral health. Different compartments of LAB were separated to analyze the effective components for growth inhibition of bacteria. Different effective sites for inhibition were found from various LAB, while the parts of cellular extract and cell wall debris were most observed to contain antimicrobial ability. The 85% cell survival rate indicated non-toxicity of LAB to cells. NO production of LPS induced inflammatory RAW264.7 was suppressed by the presence of LAB. The TNF-α production of RAW 264.7 cells were further investigated to verify the anti-inflammatory effects of LAB. While no significant reduction of TNF-α was detected among LAB treatment. In conclusion, the present studies clarified several LAB with antimicrobial activities, which were also suitable for oral health. The effective components and mechanisms of the antimicrobial effects need to be further investigated.
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