Cashew nut shell liquids exhibit antibacterial activity for control of oral biofilms

The aim was to evaluate the antibacterial and antibiofilm activity of natural (n-CNSL) and technical (t-CNSL) cashew nut shell liquid against streptococci and enterococci related to dental caries and chronic apical periodontitis, respectively.

Minimum inhibitory concentrations (MIC) and minimal bactericidal concentration (MBC) were determined to assess the antimicrobial effect of both CNSLs (n-CSNL and t-CNSL) against S. oralis ATCC 10557, S. sobrinus ATCC 6715, S. parasanguinis ATCC 903, S. mutans UA 159 and E. faecalis ATCC 19433. The antibiofilm activity was evaluated by total biomass quantification, colony forming unit (CFU) counting and scanning electron microscopy (SEM). Furthermore, cytotoxic effect of the substances was evaluated on L929 and HaCat cell lines by MTS assay.

Results of the study are:

The n-CNSL and t-CNSL showed inhibitory and bactericidal effect against all strains tested in this study, with MIC and MBC values ranging from 1.5 to 25 μg/mL. Overall, both CNSLs showed significant reduction in biomass quantification and enumeration of biofilm-entrapped cells for the strains analyzed, in biofilm formation and preformed biofilms (p < 0.05). In biofilm inhibition assay, the t-CNSL and n-CNSL showed reduction in biomass and CFU number for all bacteria, except in cell viability of S. parasanguinis treated with t-CNSL (p > 0.05). Indeed, SEM images showed a reduction in the amount of biomass, bacterial cells and changes in cellular morphology of S. mutans.

In conclusion, both substances showed effective antibacterial and antibiofilm activity against the strains used in the study, except in viability of S. parasanguinis cells treated with t-CNSL.

Thus, the researchers concluded that n-CNSL and t-CNSL exhibited antibacterial activity against oral strains on planktonic cells and biofilms, as evidenced by the reduction of biomass and cell viability, except in viability of S. parasanguinis cells treated with t-CNSL. Overall, the cytotoxic values of substances on murine fibroblast and human keratinocytes are higher than MIC and MBC values observed. Therefore, the results of this study suggest that both substances derived from cashew nuts are potential therapeutic agents against infections caused by oral bacteria.

Reference:

Cashew nut shell liquids: Antimicrobial compounds in prevention and control of the oral biofilms by Nayara de Oliveira Souza et al. published in the Archives of Oral Biology.

https://www.sciencedirect.com/science/article/abs/pii/S0003996921002624