Dental caries, associated with plaque biofilm, is highly prevalent and significantly burdens public health. Streptococcus mutans is the main cariogenic bacteria that adheres to the tooth surface and forms an abundant extracellular polysaccharide matrix (EPS) as a cariogenic biofilm scaffold. S. mutans RNase III–encoding gene ( rnc) and a putative chromosome segregation protein-encoding gene ( smc) are potentially associated with EPS production. In addition, complex interactions between S. mutans and other oral microorganisms synergistically or antagonistically affect the cariogenicity. Commensal streptococci suppress the growth of cariogenic pathogens, whereas Candida albicans mediates the formation of cariogenic biofilm through aggregation and dual-species biofilm formation with S. mutans. However, label-free detection of cariogenic microbial interactions with the EPS matrix is still challenging during laboratory investigations. Herein, we hypothesized that the S. mutans rnc-smc operon affects EPS production and aimed to observe streptococci, S. mutans, and S. mutans–C. albicans using terahertz scanning near-field optical microscopy (THz s-SNOM). The light in the 0.1- to 0.3-THz frequency range interacted with the sample through a nano-probe tip by a point-by-point scanning process. Additional noise reduction of the original image was achieved by a dual kernel Gaussian filter. The monospecies of streptococci, S. mutans smc/rnc mutants, and the dual-species of S. mutans–C. albicans were scanned by THz s-SNOM. This technique provided terahertz near-field scanning images of S. mutans smc/rnc mutants, streptococci, and dual-species of S. mutans–C. albicans. Additional analysis of the original images potentially revealed the structures of the strains, such as cell diameters and cell wall thickness. In conclusion, the results suggested that the S. mutans rnc-smc operon regulates EPS production. Furthermore, this novel label-free detection of a THz near-field scanning technique had the potential to observe the morphologies of bacterial cells and EPS matrix.

中文翻译：

---

太赫兹成像检测口腔致龋微生物域特征


与牙菌斑生物膜相关的龋齿非常普遍，对公共卫生造成严重负担。变形链球菌是主要的致龋细菌，它粘附在牙齿表面并形成丰富的细胞外多糖基质 （EPS） 作为致龋生物膜支架。变异链球菌 RNase III 编码基因 （rnc） 和推定的染色体分离蛋白编码基因 （smc） 可能与 EPS 的产生有关。此外，变形链球菌与其他口腔微生物之间的复杂相互作用协同或拮抗地影响致龋性。共生链球菌抑制致龋病原体的生长，而白色念珠菌通过与变形链球菌的聚集和双物种生物膜形成来介导致龋生物膜的形成。然而，在实验室研究期间，无标记检测致龋微生物与 EPS 基质的相互作用仍然具有挑战性。在此，我们假设变形链球菌 rnc-smc 操纵子影响 EPS 的产生，并旨在使用太赫兹扫描近场光学显微镜 （THz s-SNOM） 观察链球菌、变形链球菌和变形链球菌-白色念珠菌。0.1 至 0.3 THz 频率范围内的光通过纳米探针尖端通过逐点扫描过程与样品相互作用。原始图像的额外降噪是通过双核高斯滤波器实现的。通过 THz s-SNOM 扫描链球菌的单种、变异链球菌 smc/rnc 突变体和变异链球菌-白色念珠菌的双种。该技术提供了变形链球菌 smc/rnc 突变体、链球菌和变形链球菌-白色念珠菌双种的太赫兹近场扫描图像。 对原始图像的额外分析可能揭示了菌株的结构，例如细胞直径和细胞壁厚度。总之，结果表明变异链球菌 rnc-smc 操纵子调节 EPS 的产生。此外，这种新颖的太赫兹近场扫描技术无标记检测有可能观察细菌细胞和 EPS 基质的形态。