Petti S, Tarsitani G, Simonetti D'Arca A
G. Sanarelli Department of Public Health Sciences, Sapienza University, Piazzale Aldo Moro 5, I-00185 Rome, Italy.
Arch Oral Biol. 2008 Oct;53(10):985-90. doi: 10.1016/j.archoralbio.2008.04.009. Epub 2008 Jun 9.
Yoghurt consumption leads to a selective decrease in the oral level of mutans streptococci. It is not clear whether this decrease is due to the bactericidal activity of yoghurt or other mechanisms. The present study investigated the differences in susceptibility to yoghurt between several strains of viridans streptococci.
The sources of variation were minimised, at the expense of the external validity of the study, using culture collection strains. Each strain was tested separately on five occasions in planktonic form and logarithmic growth phase. Two strains of each of the following Streptococcus species were tested: mutans, sobrinus, gordonii, oralis, parasanguinis and sanguinis. One millilitre [10(8) colony-forming units (cfu)] of each strain was incubated (37 degrees C, 60min) with 9mL of fat-free plain yoghurt containing Streptococcus thermophilus and Lactobacillus bulgaricus (10(8) and 10(7)cfu/g, respectively) in gently vortexed tubes. Survival rates were calculated every 15min by dividing the number of viable cells, obtained using conventional laboratory procedures, by the baseline number.
Survival rates were 8% (S. mutans 6519T), 12% (S. mutans 31738), 35% (S. oralis 25671) and >50% (all other species tested) after 15min, and 0.01% (S. mutans) and >10% (all other species tested) after 30min. Overall, S. parasanguinis and S. sobrinus were the most resistant species. When heat-treated yoghurt (<10cfu/g bacteria and inactivated bacteriocins) was used, this antibacterial activity was not found.
In vitro, yoghurt with live bacteria showed selective anti-mutans activity, suggesting that the overall decrease in mutans streptococci in vivo could be due to a bactericidal effect on S. mutans but not on S. sobrinus.
食用酸奶会导致口腔中变形链球菌水平选择性下降。目前尚不清楚这种下降是由于酸奶的杀菌活性还是其他机制。本研究调查了几种草绿色链球菌菌株对酸奶敏感性的差异。
以牺牲研究的外部效度为代价，使用培养保藏菌株将变异来源降至最低。每种菌株在浮游形式和对数生长期分别进行了5次测试。对以下每种链球菌属的两个菌株进行了测试：变形链球菌、远缘链球菌、戈氏链球菌、口腔链球菌、副血链球菌和血链球菌。将每种菌株的1毫升[10(8)菌落形成单位（cfu）]与9毫升不含脂肪的普通酸奶（分别含有嗜热链球菌和保加利亚乳杆菌，10(8)和10(7)cfu/g）在轻轻涡旋的试管中孵育（37℃，60分钟）。每隔15分钟通过将使用传统实验室程序获得的活细胞数除以基线数来计算存活率。
15分钟后存活率分别为8%（变形链球菌6519T）、12%（变形链球菌31738）、35%（口腔链球菌25671）和>50%（所有其他测试菌株），30分钟后为0.01%（变形链球菌）和>10%（所有其他测试菌株）。总体而言，副血链球菌和远缘链球菌是最具抗性的菌株。使用热处理酸奶（<10cfu/g细菌且细菌素失活）时，未发现这种抗菌活性。
在体外，含有活细菌的酸奶表现出选择性抗变形链球菌活性，这表明体内变形链球菌的总体减少可能是由于对变形链球菌而非远缘链球菌的杀菌作用。
