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

Abstract

The continuous spread of antimicrobial resistance is endangering the efficient control of enterotoxigenic Escherichia coli (ETEC), which is mainly responsible for post-weaning diarrhea onset in piglets. Thymol, the key constituent of thyme essential oil, is already used in animal nutrition for its antimicrobial action. The aim of this study was to investigate the potential adjuvant effect of thymol to re-establish antibiotic efficacy against highly resistant ETEC field strains. Secondly, we evaluated the modulation of virulence and antibiotic resistance genes. Thymol showed the capacity to control ETEC growth and, when combined with ineffective antibiotics, it increased their antimicrobial power. In particular, it showed significant effects when blended with colistin and tetracycline, suggesting that the adjuvant effects rely on the presence of complementary mechanisms of action between molecules, or the absence of resistance mechanisms that inactivate antibiotics and target sites. Furthermore, our findings demonstrate that, when added to antibiotics, thymol can help to further downregulate several virulence and antibiotic resistance genes, offering new insights on the potential mechanisms of action. Therefore, in a one-health approach, our study supports the beneficial effects of combining thymol with antibiotics to restore their efficacy, together with the possibility of targeting gene expression as a pioneering approach to manage ETEC pathogenicity.

Botanicals as a zinc oxide alternative to protect intestinal cells from an Escherichia coli F4 infection in vitro by modulation of enterocyte inflammatory response and bacterial virulence

“…Other than modulating cellular inflammatory response, thymol deeply influences bacterial virulence genes expression ( 65 , 66 ). Several studies demonstrated how thymol not only limits bacterial growth, but also controls E. coli F4 quorum sensing effectors, reducing ETEC ability to target intestinal cells ( 29 , 67 ). This secondary mechanism of action against pathogens could explain why ThyEO did not exert extensive effects on Caco-2 cells, though keeping high TER values.…”

Encapsulation of Thymol in Gelatin Methacryloyl (GelMa)-Based Nanoniosome Enables Enhanced Antibiofilm Activity and Wound Healing

“…Especially in the last two decades, many in vitro studies have been performed to approve the antimicrobial features of Thymol [ 8 ]. Since many antibiotic agents lose efficacy after a certain time of treatment, a combination of nature-based compounds such as Thymol can be beneficial [ 9 ]. Further, Thymol can downregulate virulence and antibiotic resistance genes when combined with antibiotics [ 9 ].…”

“…Since many antibiotic agents lose efficacy after a certain time of treatment, a combination of nature-based compounds such as Thymol can be beneficial [ 9 ]. Further, Thymol can downregulate virulence and antibiotic resistance genes when combined with antibiotics [ 9 ]. Thymol (2-isopropyl-5-methylphenol) is a monoterpene compound with proven effects on a variety of pathogenic bacteria, including S. aureus , E. coli , Listeria monocytogenes , and Shigella sonnei [ 10 ].…”