Evaluation of Combined Antibacterial Effects of Eugenol, Cinnamaldehyde, Thymol, and Carvacrol against E. coli with an Improved Method

Abstract

In this study, the antibacterial activities of eugenol, cinnamaldehyde, thymol, carvacrol, and their combinations against E. coli were investigated separately. First, broth macro-dilution assay was adopted to determine the minimal inhibitory concentration (MIC) of the 4 components. Second, the combination testing was performed using chequerboard method. Finally, the combined effects were evaluated with an improved method, which was based on the indices of fractional inhibitory concentration (FIC) and Effect of the Combination (EC) jointly. The results indicated that MICs of the 4 components were 1600, 400, 400, and 400 mg/L, respectively; treatments with cinnamaldehyde/eugenol, thymol/eugenol, carvacrol/eugenol, and thymol/carvacrol revealed synergistic effects according to the 2 indices. By means of combination, MICs of eugenol, cinnamaldehyde, thymol, and carvacrol decreased to 400, 100, 100, and 100 mg/L, respectively. Consequently, the negative impacts of unpleasant smell of these 4 components could be minimized, making it possible to add them to foods as preservatives. In addition, this improved evaluation method provided a more accurate and comprehensive way to evaluate combined effects.

Synergistic effects of floral phytochemicals against a bumble bee parasite

“…Combinations of thymol and eugenol had synergistic effects against Escherichia coli (Pei, Zhou, Ji, & Xu, 2009), but antagonistic effects against Crithidia fasciculata (Azeredo & Soares, 2013). However, compounds with similar or overlapping targets typically have additive effects (Jia et al., 2009).…”

Versatile and Synergistic Potential of Eugenol: A Review

“…Eugenol exhibited synergistic interaction with vancomycin, gentamicin and β-lactam antibiotics lead to greater antimicrobial effect [28,32]. Eugenol also exhibited synergic interactions with cinnamate, cinnamaldehyde, thymol and carvacrol, resulting greater antibacterial activity [33][34]. Sub-inhibitory concentrations of eugenol (16-128 µg/ mL) dose-dependently decreased the necrosis factor-inducing and haemolytic activities of culture supernatants and significantly reduced the production of staphylococcal enterotoxin A [35].…”

Inactivation Kinetics ofVibrio parahaemolyticuson Sand Shrimp(Metapenaeus ensis)by Cinnamaldehyde at 4°C

“…Zhang et al [23] reported that two identical peaks appeared with bacteria alone (i.e., L. monocytogenes ATCC 19115 and E. coli) but disappeared with cinnamaldehyde treatments by the UPLC (Ultra Performance Liquid Chromatography) system, which is different from the other three natural antimicrobials, namely, thymol, eugenol, and carvacrol. The two peaks are suspected to be two identical metabolic products related to quorum-sensing pathways [32], since Pei et al [18] hypothesized that the arbonyl group on cinnamaldehyde may adhere to proteins to prevent the action of amino acid decarboxylases [33]; Niu et al [34] reported that cinnamaldehyde would influence signaling pathways of quorum sensing by interfering with the binding of 3-hydroxy-C4, 3-oxo-C6-HSL, and AI-2 synthetic pathway and Brackman et al [35] discovered that cinnamaldehyde interferes with AI-2 based quorum sensing by decreasing the DNA-binding ability of LuxR to bind to its target promoter sequence.…”

“…Moreover, due to the vast usage of antibiotics worldwide, the accumulation of antibiotic-resistant bacteria and genes, leading to the treatment failure or longer convalescence in both humans and animals, studies on antibiotic replacement are currently emerging [18]. Use of natural antimicrobials, such as extracts from spices and herbs for the purpose of food preservation or the substitution of antibiotics, has arisen.…”