Thymol tolerance in Escherichia coli induces morphological, metabolic and genetic changes

Abstract

BackgroundThymol is a phenolic compound used for its wide spectrum antimicrobial activity. There is a limited understanding of the antimicrobial mechanisms underlying thymol activity. To investigate this, E. coli strain JM109 was exposed to thymol at sub-lethal concentrations and after 16 rounds of exposure, isolates with a 2-fold increased minimal inhibitory concentration (MIC) were recovered (JM109-Thyr). The phenotype was stable after multiple sub-cultures without thymol.ResultsCell morphology studies by scanning electron microscopy (SEM) suggest that thymol renders bacterial cell membranes permeable and disrupts cellular integrity. 1H Nuclear magnetic resonance (NMR) data showed an increase in lactate and the lactic acid family amino acids in the wild type and JM109-Thyr in the presence of thymol, indicating a shift from aerobic respiration to fermentation. Sequencing of JM109-Thyr defined multiple mutations including a stop mutation in the acrR gene resulting in a truncation of the repressor of the AcrAB efflux pump. AcrAB is a multiprotein complex traversing the cytoplasmic and outer membrane, and is involved in antibiotic clearance.ConclusionsOur data suggests that thymol tolerance in E. coli induces morphological, metabolic and genetic changes to adapt to thymol antimicrobial activity.

Biogenic Silver Nanoparticles Strategically Combined With Origanum vulgare Derivatives: Antibacterial Mechanism of Action and Effect on Multidrug-Resistant Strains

“…Thy and bioAgNP alone significantly caused ROS production in E. coli compared to the untreated control, in line with other studies (Kim et al, 2011;Li et al, 2014;Ninganagouda et al, 2014;Shen et al, 2016;Yan et al, 2018;Al-Kandari et al, 2019); the combination of Thy and bioAgNP also increased ROS production by E. coli. In addition to protein oxidation, lipid oxidation also occurred.…”

“…In this study, exactly at the beginning of treatment with Thy (0 h), E. coli produced significantly higher amount of ROS than the untreated control (Figure 3A). Although the antioxidant activity of Thy has been reported on animal cells (Chauhan and Kang, 2014;Coccimiglio et al, 2016;Nagoor Meeran et al, 2017), some studies have shown that its antimicrobial activity involves ROS production (Shen et al, 2016;Al-Kandari et al, 2019). Yuan et al (2018) showed that genes related to oxidative stress defense were upregulated in Thy-treated E. coli O157:H7.…”

Terpenes as bacterial efflux pump inhibitors: A systematic review

“…On the other hand, Wu et al (2008) showed that andrographolide alone or combined with standard drugs induced no change in gene expression. The mechanism of action of the monoterpene thymol ( Al-Kandari et al, 2019 ) was associated with the alteration of the membrane permeability and induction of genetic and morphological changes that lead to inhibition of the expression of AcrAB-TolC efflux pump in Escherichia coli. Accordingly, Lorenzi et al (2009) showed that the terpene geraniol inhibited chloramphenicol’s efflux, which was mediated by the AcrAB-TolC system.…”

Thymol as an Adjuvant to Restore Antibiotic Efficacy and Reduce Antimicrobial Resistance and Virulence Gene Expression in Enterotoxigenic Escherichia coli Strains

“…It is demonstrated that thymol exerts its antimicrobial power by permeabilizing and depolarizing bacterial membranes thanks to its pore-forming activity [ 18 , 43 ]. Despite the similarity of its mechanism of action with several antibiotics, resistance determinants do not currently seem to affect thymol or other nature-identical compounds [ 44 ]. For this reason, the aim of this study was to investigate if thymol, as a representative of nature-identical compounds, could re-establish the efficacy of conventional antibiotics by exerting an adjuvant effect.…”