Chui Chanthoeun, Hiratsuka Koichi, Aoki Akira, Takeuchi Yasuo, Abiko Yoshimitsu, Izumi Yuichi
Department of Periodontology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
Lasers Surg Med. 2012 Dec;44(10):856-64. doi: 10.1002/lsm.22090. Epub 2012 Nov 5.
Blue light has been employed or investigated in both the medical and dental fields. Many studies have so far been reported a bactericidal effect of blue light emitting diodes (LED). However, it is still unclear whether exposure to blue LED kills or inhibits the growth of bacteria. We therefore investigated the effect of blue LED irradiation on the growth of Porphyromonas gingivalis compared with the effects of red LED.
P. gingivalis cell suspensions were irradiated with blue or red LED (135 J/cm2) anaerobically, incubated for various lengths of time, and then the total RNAs were isolated. The RNA degradation and gene expression levels of stress-related proteins in blue or red LED-irradiated samples were examined using the RNA integrity number (RIN) and RT-PCR, respectively. Quantitative RT-PCR was done to investigate the gene expression profiles associated with chromosome replication and cell division.
Exposure to blue LED delayed the growth of P. gingivalis, while red LED did not. The RIN value indicated no RNA degradation in either the blue or red LED-irradiated samples. In addition, the gene expression levels of stress-related molecules remained either constant or increased 15 minutes after the blue LED irradiation compared to that before irradiation, thus suggesting that blue LED may not kill P. gingivalis cells. However, the blue LED irradiation did lead to a remarkably decreased expression of genes associated with chromosomal DNA replication and cell division after 5 minutes; exposure to the red LED did not.
The inhibition of the growth of P. gingivalis by blue LED may therefore be induced not by a bactericidal effect, but instead due to a bacteriostatic effect mediated by the suppression of the genes associated with chromosomal DNA replication and cell division at the transcriptional level.
蓝光已在医学和牙科领域得到应用或研究。迄今为止，许多研究报道了蓝光发光二极管（LED）的杀菌作用。然而，蓝光LED照射是否会杀死或抑制细菌生长仍不清楚。因此，我们研究了蓝光LED照射对牙龈卟啉单胞菌生长的影响，并与红光LED的作用进行比较。
牙龈卟啉单胞菌细胞悬液在厌氧条件下用蓝光或红光LED（135 J/cm²）照射，孵育不同时间，然后分离总RNA。分别使用RNA完整性数值（RIN）和逆转录聚合酶链反应（RT-PCR）检测蓝光或红光LED照射样品中RNA降解情况以及应激相关蛋白的基因表达水平。进行定量RT-PCR以研究与染色体复制和细胞分裂相关的基因表达谱。
蓝光LED照射会延迟牙龈卟啉单胞菌的生长，而红光LED则不会。RIN值表明蓝光或红光LED照射样品中均无RNA降解。此外，与照射前相比，蓝光LED照射15分钟后应激相关分子的基因表达水平保持不变或升高，这表明蓝光LED可能不会杀死牙龈卟啉单胞菌细胞。然而，蓝光LED照射5分钟后，与染色体DNA复制和细胞分裂相关的基因表达显著降低；红光LED照射则无此现象。
因此，蓝光LED对牙龈卟啉单胞菌生长的抑制作用可能不是由杀菌作用引起的，而是由转录水平上抑制与染色体DNA复制和细胞分裂相关的基因介导的抑菌作用所致。
