Antibacterial effect of cinnamaldehyde in a microemulsion system against oral colonizing biofilms

In the oral biofilm there are the presence of Streptococcus mutans, which is considered the main microorganism related to caries, and Streptococcus mitis and Streptococcus oralis that are considered commensal microorganisms. Mechanical disorganization of the biofilm associated with antimicrobial agents represents an effective method of injury prevention. Thus, the aim of this study was to evaluate the antibacterial effect of cinnamaldehyde-loaded microemulsion formulated in the presence (CEQ) and absence (CE) of chitosan. Single-species biofilms of S. mutans (UA159), S. mitis (ATCC 903) and S. oralis (ATCC 49456) were staggered (108 CFU/mL) and seeded in 96-well plates in BHI medium + 1% sucrose. The samples were incubated for 24 h and 48 h and then remained exposed for 24 h to CE and CEQ microemulsions. Microemulsions were produced by sonicator using cinnamaldehyde (1-10%). The concentration of chitosan included in the microemulsions was 0.1%. 0.12% chlorhexidine and BHI medium + 1% sucrose were used as positive and negative controls, respectively. Subsequently, an analysis of cellular metabolism was performed using the MTT test. Data were analyzed by Kruskal-Wallis test (α=5%). For S. oralis at 24 h, it was assumed that the 2.5% and 1% CE system showed activity similar to chlorhexidine (p>0.05). For the other biofilms, the effect of all concentrations of the CE and CEQ systems showed lower antimicrobial activity than chlorhexidine 0.12% (p<0.05). At 48 h, all microemulsion also showed lower activity than chlorhexidine (p<0.05). The antibacterial activity of cinnamaldehyde-loaded microemulsions was not dependent on concentration but varied according to the tested microorganism. The chitosan-based systems had low antimicrobial activity.