Carvacrol exhibits rapid bactericidal activity against Streptococcus pyogenes through cell membrane damage

Niluni M Wijesundara,Zhenyu Cheng,H P Vasantha Rupasinghe,Song F Lee,Ross Davidson

doi:10.1038/s41598-020-79713-0

Abstract

Streptococcus pyogenes is an important human pathogen worldwide. The identification of natural antibacterial phytochemicals has renewed interest due to the current scarcity of antibiotic development. Carvacrol is a monoterpenoid found in herbs. We evaluated carvacrol alone and combined with selected antibiotics against four strains of S. pyogenes in vitro. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of carvacrol against S. pyogenes were 125 µg/mL (0.53 mM) and 250 µg/mL (1.05 mM), respectively. Kill curve results showed that carvacrol exhibits instantaneous bactericidal activity against S. pyogenes. We also demonstrated the potential mechanism of action of carvacrol through compromising the cell membrane integrity. Carvacrol induced membrane integrity changes leading to leakage of cytoplasmic content such as lactate dehydrogenase enzymes and nucleic acids. We further confirmed dose-dependent rupturing of cells and cell deaths using transmission electron microscopy. The chequerboard assay results showed that carvacrol possesses an additive-synergistic effect with clindamycin or penicillin. Carvacrol alone, combined with clindamycin or penicillin, can be used as a safe and efficacious natural health product for managing streptococcal pharyngitis.

Highlights

Streptococcus pyogenes is an important human pathogen worldwide
Penicillin remains the first choice of drug for S. pyogenes, other antibiotics are shown to be effective in eradicating S. pyogenes
We investigated the antimicrobial activity of carvacrol against S. pyogenes and attempted to understand the potential mechanisms of action

Summary

Introduction

Streptococcus pyogenes is an important human pathogen worldwide. The identification of natural antibacterial phytochemicals has renewed interest due to the current scarcity of antibiotic development. Carvacrol alone, combined with clindamycin or penicillin, can be used as a safe and efficacious natural health product for managing streptococcal pharyngitis. Antibiotic therapy is imperative to eradicate S. pyogenes from the throat in order to decrease the risk of transmission[15] and to prevent some of the suppurative and non-suppurative complications[16]. Despite the genetic diversity of S. pyogenes and the massive exposure over several decades, the organism remains sensitive to penicillin and other commonly used beta-lactam antibiotics. Beta-lactam antibiotics exhibit bactericidal effects by inhibiting the synthesis of bacterial cell w alls[18]. They prevent cross-linking between peptidoglycan chains through the DD-transpeptidase enzyme, known as a penicillin-binding p rotein[19]. Macrolide resistance has been well described either due to active efflux (mef genes) or target modification (erm genes)[20,21]

Objectives

Methods

Results

Discussion

Conclusion