Bactericidal activity and oral pathogen inactivation by electromagnetic wave irradiation

Aims: The aim of this work was to clarify the effects of electromagnetic wave irradiation (EMWI) on oral bacterial pathogens. Methods and Results: A Gram‐negative (Porphyromonas gingivalis) or Gram‐positive (Streptococcus mutans, S. intermedius, Enterococcus faecalis) bacterial suspension was irradiated by EMW apparatus (500–1000 kHz, 5–15 times, 1 s time^?1). Quantification of survival bacteria by CFU counting revealed that EMWI exhibited marked bactericidal activity against all tested bacteria and bactericidal activity at 500 kHz increased in an irradiation number‐dependent manner. After EMWI at 500 kHz, scanning electron microscopic observations showed that the chain of S. mutans cells was shortened after 5 irradiations and the outlines of bacterial cells (S. mutans and P. gingivalis) were unclear after 5–10 irradiations. EMWI inhibited the inductive effect of S. mutans on pro‐inflammatory cytokine production in human monocytes and this inhibitory effect was comparable with that of heat‐killed bacteria. Furthermore, using an enzyme activity assay, EMWI partially inactivated the activities of gingipains from P. gingivalis. Conclusions: These findings demonstrated that EMWI has inactivation and bactericidal activities against single microbial species among four kinds of oral pathogens. Significance and Impact of the Study: Electromagnetic wave irradiation may be applicable for medical disinfection and sterilization, such as refractory periapical periodontitis.