Abstract
This study sets out to compare the antibacterial and antibiofilm profiles of Ci/Ca EOs alone and in combination together against infectious bacterial strains. MIC assay was carried out to survey the effectiveness of prepared EOs by two-fold serial dilution method and MTT evaluation. Synergic antibacterial properties of EOs against target strains were studied by using checkerboard titration method. Biofilm growth and development were evaluated using CV and XTT reduction assays. Antibacterial activity was observed for EOs against both bacterial strains with stronger activity for CiEO against both bacteria. The synergistic antibacterial effect was observed only against B. subtilis. Based on the FIC index, combinations could not inhibit the growth of E. coli. The pure EOs and their combination inhibited cell attachment for both studied bacteria with stronger effect on E. coli. CV and XTT reduction assays results showed that Ci EO and its combination with CaEO had the highest antibiofilm activity at lowest MIC value 0.08% and 0.04/0.02% against biofilm formed by E. coli and B. subtilis respectively, indicating a high antibiofilm potential. Computational docking analyses also postulated that the active constituents of evaluated EOs have the potential to interact with different bacterial targets, suggested binding mode of action of EOs metabolites. By and large, synergistic anti-biofilm properties of EOs may provide further options for developing novel formula to inhibit a variety of infectious clinical and industrial strains without (or less) toxicity effects on human body.Graphical
Highlights
Today, finding promising natural and synthetic agents with potential anti-bacterial activity is becoming so popular among scientists
Inhibition of initial bacteria cell attachment The results of anti-adhesion tests conducted with the crystal violet assay showed that Cinnamon essential oils (EO) (CiEO) inhibited cell attachment of E. coli completely (100% inhibition activity), while Cardamom EO (CaEO) and their combination (1/64 minimum inhibitory concentration (MIC) of cardamom + 1/2 MIC of cinnamon) displayed 92% and 62% inhibition against E. coli, respectively (Table 3)
It seems quite clear that EOs are including considerable volume of purified secondary metabolites that can enter bacterial communities or cells to interact with a variety of molecular targets, leading to gradual inhibition of bacterial growth (Kerekes et al 2019; Zhang et al 2018)
Summary
Today, finding promising natural and synthetic agents with potential anti-bacterial activity is becoming so popular among scientists. A variety of plant extracts (or essential oils) and chemical substances have been evaluated to identify their toxicity profiles on infectious organisms (Zarayneh et al 2018). Biofilm is a mixture of various groups of microorganisms in a complex with extracellular polymer matrix in which cells bind tightly together on various surfaces (Wang et al 2020). Biofilm usually creates a sticky gel composed of polysaccharides, proteins and other organic components on a wet surface, that occur in different clinical, industrial and food processing environments and cause serious problems including cross contamination of food products (Muslim et al 2018). Bacterial biofilms are inherently more tolerant to antibiotic therapies and chemical agents compared with planktonic cells in suspension (Felipe et al 2019)
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