Oral Biology and Biochemistry Laboratory, Institute for Research in Dental Sciences, Faculty of Dentistry, University of Chile, Santiago, Chile.
Cariology Unit, Department of Oral Rehabilitation, University of Talca, Talca, Chile.
Caries Res. 2019;53(2):194-203. doi: 10.1159/000490950. Epub 2018 Aug 14.
Streptococcus mutans synthesizes 3 glucosyltransferases (Gtfs) associated with cariogenic biofilms, while commensal Streptococcus sanguinis produces only one; gtfP and hydrogen peroxide (H2O2) by SpxB. The aim was to test the hypothesis that under a sucrose-induced cariogenic challenge, the expression of competition-related genes is differentially regulated depending on whether S. sanguinis or S. mutans primarily colonize enamel. Dual-species biofilms of S. sanguinis and S. mutans were formed under different colonization sequences on enamel slabs and exposed to 10% sucrose for 5 min, 3×/day for 5 days. Biofilms were analyzed for the transcriptional response of competition-related genes encoding gtfB, gtfC, and gtfD for S. mutans and gtfP and spxB for S. sanguinis. In addition, acidogenicity (pH) and viable cells in each of the conditions were determined. For all the genes, a downregulation was observed during simultaneous colonization by both bacterial species. In contrast, gtfB was upregulated when S. sanguinis was the first colonizer (p < 0.05). Both gtfC and gtfD were upregulated during sequential inoculation with S. sanguinis as the first colonizer. An eleven-fold upregulation of gtfP was observed in biofilms with S. mutans as initial colonizer (p < 0.05), with a moderate increase in spxB expression. The lowest pH values and viable cells of S. sanguinis were observed when S. mutans first colonized the enamel slabs, compared to the other conditions (p < 0.05). Demanding sucrose-challenged oral environment requires increased expression of virulence traits to effectively compete and thrive in the dental biofilm, especially when the competitor has already colonized the ecological niche.
变形链球菌合成 3 种与致龋生物膜相关的葡糖基转移酶（Gtfs），而共生的血链球菌仅产生 1 种；gtfP 和 H2O2 由 SpxB 产生。目的是检验以下假设：在蔗糖诱导的致龋挑战下，竞争相关基因的表达是否根据 S. sanguinis 或 S. mutans 主要定植在牙釉质上而有所不同。在牙釉质平板上以不同的定植顺序形成 S. sanguinis 和 S. mutans 的双种生物膜，然后用 10%蔗糖暴露 5 分钟，每天 3 次，持续 5 天。分析生物膜中编码 S. mutans 的竞争相关基因 gtfB、gtfC 和 gtfD 以及 S. sanguinis 的 gtfP 和 spxB 的转录反应。此外，还测定了每种条件下的产酸（pH）和活菌数。所有基因在两种细菌同时定植时均下调。相比之下，当 S. sanguinis 是第一个定植菌时，gtfB 上调（p < 0.05）。当 S. sanguinis 首先接种时，gtfC 和 gtfD 均上调。当 S. mutans 作为初始定植菌时，gtfP 上调 11 倍（p < 0.05），spxB 表达适度增加。当 S. mutans 首先定植牙釉质平板时，观察到 S. sanguinis 的最低 pH 值和活菌数，与其他条件相比（p < 0.05）。在口腔中，蔗糖负荷的环境需要增加毒力特征的表达，以有效地在牙菌斑中竞争和繁殖，尤其是当竞争者已经定植在生态位上时。
