Myrtenol Attenuates MRSA Biofilm and Virulence by Suppressing sarA Expression Dynamism

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is a deleterious human pathogen responsible for severe morbidity and mortality worldwide. The pathogen has attained high priority in the World Health Organization (WHO) – Multidrug-resistant (MDR) pathogens list. Emerging MDR strains of S. aureus are clinically challenging due to failure in conventional antibiotic therapy. Biofilm formation is one of the underlying mechanisms behind the antibiotic resistance. Hence, attenuating biofilm formation has become an alternative strategy to control persistent infections. The current study is probably the first that focuses on the antibiofilm and antivirulence potential of myrtenol against MRSA and its clinical isolates. Myrtenol exhibited a concentration-dependent biofilm inhibition without causing any harmful effect on cell growth and viability. Further, microscopic analysis validated the biofilm inhibitory efficacy of myrtenol against MRSA. In addition, myrtenol inhibited the synthesis of major virulence factors including slime, lipase, α-hemolysin, staphyloxanthin and autolysin. Inhibition of staphyloxanthin in turn sensitized the MRSA cells to healthy human blood and hydrogen peroxide (H2O2). Notably, myrtenol treated cells were deficient in extracellular DNA (eDNA) mediated autoaggregation as eDNA releasing autolysis was impaired by myrtenol. Biofilm disruptive activity on preformed biofilms was observed at concentrations higher than minimum biofilm inhibitory concentration (MBIC) of myrtenol. Also, the non-cytotoxic effect of myrtenol on human peripheral blood mononuclear cell (PBMC) was evidenced by trypan blue and Alamar blue assays. Transcriptional analysis unveiled the down-regulation of global regulator sarA and sarA mediated virulence genes upon myrtenol treatment, which is well correlated with results of phenotypic assays. Thus, the results of the present study revealed the sarA mediated antibiofilm and antivirulence potential of myrtenol against MRSA.

Antibacterial and Antibiofilm Activity of Myrtenol against Staphylococcus aureus

“…Similar results of myrtenol antibiofilm activity were found by Selvaraj et al [ 14 ], whose data show that myrtenol attenuates MRSA biofilm considerably, in addition to inhibiting the production of major virulence factors of MRSA, such as lipase, hemolysin and staphyloxanthin. In addition, it affected the slime synthesis, autoaggregation, autolysis, and eDNA production in MRSA.…”

“…As part of the context of natural products, myrtenol is a phytoconstituent present in Myrtus communis L. (Myrtaceae) essential oil [ 9 ], which ethnopharmacological studies revealed to be used in folk medicine for several purposes, including antimicrobial [ 10 ]. Although anxiolytic [ 11 ], anti-inflammatory [ 12 ] and gastroprotective [ 13 ] activity of isolated myrtenol has been reported; its antibacterial and antibiofilm potential is still poorly described [ 14 ]. Given these facts, this study aimed to investigate the myrtenol activity against S. aureus , also analyzing its effect in combination with conventional antibacterial drugs.…”

sarA-Dependent Antibiofilm Activity of Thymol Enhances the Antibacterial Efficacy of Rifampicin Against Staphylococcus aureus

“…Notably, antibiofilm agents are reported to potentiate the efficacy of antibiotics against bacterial biofilm when combined with antibiotics. Plenty of compounds with antibiofilm activity have been identified from various natural resources so far ( Abraham et al, 2012 ; Sethupathy et al, 2016 , 2017 ; Selvaraj et al, 2019 ; Valliammai et al, 2019 ). Thymol is a major constituent in the essential oil of thyme plant ( Thymus vulgaris ), and it is known to have various biological properties such as antibacterial, antifungal, antioxidant, and cognitive-enhancing activities ( Braga, 2005 ; Tohidpour et al, 2010 ; Azizi et al, 2012 ).…”

Glabridin Averts Biofilms Formation in Methicillin-Resistant Staphylococcus aureus by Modulation of the Surfaceome

“…To date, several environmental factors such as glucose, salt (NaCl), ethanol, high temperature, antibiotics stress, and low oxygen have been described to support biofilm formation in S. aureus ( Jefferson, 2004 ; Fitzpatrick et al, 2005 ). Recent studies have focused on the development of antimicrobial drugs to inhibit the formation of biofilm and/or other virulence factors which appear promising with regards to controlling bacterial infections without spreading resistance ( Lee et al, 2013 , 2014 , 2016 ; Phuong et al, 2017 ; Kong et al, 2018 ; Selvaraj et al, 2019 ).…”