Effects of a sub-minimum inhibitory concentration of chlorhexidine gluconate on the development of <i>in vitro</i> multi-species biofilms

Following antimicrobial administrations in oral environments, bacteria become exposed to a sub-minimum inhibitory concentration (sub-MIC), which can induce <i>in vitro</i> single-species biofilms. This study explored the effects of chlorhexidine gluconate (CHG) at a sub-MIC on <i>in vitro</i> multi-species biofilms comprising <i>Streptococcus mutans</i>, <i>Streptococcus oralis</i> and <i>Actinomyces naeslundii</i>. CHG at a sub-MIC was found to induce <i>in vitro</i> biofilm growth, although the bacterial growth was not significantly different from that in the control. The gene transcription related to <i>S. mutans</i> multi-species biofilm formation with CHG at a sub-MIC was significantly higher than that of the control, but this was not found in <i>S. mutans</i> single-species biofilms. The bio-volume of extracellular polysaccharides with CHG at a sub-MIC was significantly higher than that of the control. This suggests that CHG at a sub-MIC may promote the development of multi-species biofilms by affecting the gene transcription related to <i>S. mutans</i> biofilm formation.