Terpenoids as Natural Agents against Food-Borne Bacteria—Evaluation of Biofilm Biomass versus Viability Reduction

Abstract

This study aimed to analyse the antibacterial potential of limonene, terpineol, and eugenol for the biofilm reduction of food-borne E. coli, S. aureus and S. typhimurium. A microdilution test with resazurin application was used for the minimum inhibitory concentration and a colony plate count was used for the minimum bactericidal concentration. Biofilm biomass was quantified using the crystal violet assay, while biofilm viability was determined using the plate count method. The results show the highest antibacterial potential among terpenoids for eugenol, followed by terpineol and limonene. Both biomass reduction and viability are strongly dependent on the concentration of all terpenoids tested (p < 0.05). Moreover, eugenol reduced biofilm biomass most effectively (67% for E. coli), while viability was reduced most by terpineol (3.8 log CFU cm−2 for E. coli and S. aureus). The correlation coefficient for the reduction in biomass and viability was highest for eugenol (0.9) and chlorhexidine for all bacteria tested, while the lowest correlation was found for limonene (0.6). Results also demonstrate that tested terpenoids are effective as standard antimicrobial agent chlorhexidine. This suggests that eugenol has potential against food-borne biofilms as it simultaneously reduces both biomass and viability of biofilms.