title: Blue LED inhibits the growth of Porphyromonas gingivalis by suppressing the expression of genes associated with DNA replication and cell division.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Periodontology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Chanthoeun
authors.initials: C
authors.lastname: Chui
authors.forename: Koichi
authors.initials: K
authors.lastname: Hiratsuka
authors.forename: Akira
authors.initials: A
authors.lastname: Aoki
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Takeuchi
authors.forename: Yoshimitsu
authors.initials: Y
authors.lastname: Abiko
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Izumi
mesh_terms: D002455:Cell Division / Q000187:drug effects / Q000528:radiation effects*; D003116:Color; D004261:DNA Replication / Q000235:genetics / Q000528:radiation effects*; D004269:DNA, Bacterial; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000528:radiation effects*; D008027:Light; D016966:Porphyromonas gingivalis / Q000235:genetics / Q000254:growth & development / Q000528:radiation effects*; D012329:RNA, Bacterial; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D004269:DNA, Bacterial; D012329:RNA, Bacterial