McNeill Karol, Hamilton I R
Department of Oral Biology, Faculty of Dentistry, University of Manitoba, 780 Bannatyne Ave., Winnipeg, MB, Canada R3E 0W2.
FEMS Microbiol Lett. 2003 Apr 11;221(1):25-30. doi: 10.1016/S0378-1097(03)00164-2.
Streptococcus mutans, a major etiological agent of dental caries, is a component of the dental plaque biofilm and functions during caries progression in acidic lesions that may be at or below pH 4. In this study, we were interested in determining the acid tolerance of 1-7-day chemostat-grown biofilm cells of S. mutans BM71 growing in a semi-defined medium at a rate consistent with that of cells in dental plaque (dilution rate=0.1 h(-1)), as well as, assessing the capacity of 2- and 5-day biofilms to induce an acid tolerance response that would enhance survival at a killing pH (3.5). As expected, biofilm cell growth increased (2.5-fold) from day 1 to day 7 (10.6-25.7 x 10(6) cells cm(-)(2)) with the percentage live cells over that period averaging 79.4%, slightly higher than that of planktonic cells (77.4%). Biofilms were highly resistant to acid killing at pH 3.5 for 2 h with survival ranging from 41.8 (1 day) to 63.9% (7 day), while the percentage of live cells averaged 43.4%. Planktonic and dispersed biofilm cells were very acid-sensitive with only 0.0009%- and 0.0002-0.2% survivors, respectively. Unlike the planktonic cells, the incubation of 2- and 5-day biofilms at pH 5.5 for periods of up to 6 h induced strong acid tolerance responses that enhanced survival during a subsequent exposure to acid killing at pH 3.5.
变形链球菌是龋齿的主要病原体，是牙菌斑生物膜的一个组成部分，在pH值可能等于或低于4的酸性病变的龋齿进展过程中发挥作用。在本研究中，我们感兴趣的是确定在半限定培养基中以与牙菌斑中细胞一致的速率（稀释率 = 0.1 h⁻¹）生长1 - 7天的恒化器培养的变形链球菌BM71生物膜细胞的耐酸性，以及评估2天和5天生物膜诱导耐酸性反应的能力，该反应将提高在致死pH值（3.5）下的存活率。正如预期的那样，生物膜细胞生长从第1天到第7天增加了2.5倍（从10.6 - 25.7×10⁶个细胞/cm²），在此期间活细胞百分比平均为79.4%，略高于浮游细胞（77.4%）。生物膜在pH 3.5下2小时对酸杀伤具有高度抗性，存活率范围为41.8%（1天）至63.9%（7天），而活细胞百分比平均为43.4%。浮游和分散的生物膜细胞对酸非常敏感，存活率分别仅为0.0009%和0.0002% - 0.2%。与浮游细胞不同，2天和5天生物膜在pH 5.5下孵育长达6小时会诱导强烈的耐酸性反应，从而提高在随后暴露于pH 3.5的酸杀伤时的存活率。
