Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) is a serious human pathogen which has been listed as a high-priority multi-drug resistance pathogen by the World Health Organization (WHO). Persistent MRSA infections are often associated with biofilm formation and resistance to conventional antimicrobial therapy. Inhibiting the surface adherence and the virulence of the bacterium is the current alternative approach without affecting growth to reduce the possibility of resistance development. Although numerous antibiofilm agents have been identified, their mode of action remains unclear. Combining two drugs with different modes of action will improve the efficiency of the treatment strategy against MRSA. The present study was aimed to decipher the molecular mechanism underlying the antibiofilm activity of thymol against MRSA and assess the ability of thymol to improve the antibacterial activity of rifampicin. Thymol significantly inhibited 88% of MRSA biofilm formation at 100 μg/ml and reduced the surface adherence of MRSA on glass, stainless steel, and titanium surface coated with human plasma as evidenced by microscopic analyses. qPCR analysis of global virulence regulatory genes and biofilm assay with S. aureus wild type, ΔsarA, and Δagr strains revealed the sarA-mediated antibiofilm activity of thymol and inhibition of sarA-controlled virulence factors. Congo red assay and erythrocyte lysis assay further confirmed the reduction in polysaccharide intracellular adhesin and hemolysin. Importantly, thymol enhanced the antibacterial and the biofilm eradication efficiency of rifampicin against MRSA and also reduced the formation of persisters. Thus, the present study reveals the sarA-dependent antibiofilm efficacy of MRSA and suggests thymol as the promising combinatorial candidate in potentiating the antibacterial activity of rifampicin against persistent MRSA infections.
Highlights
Staphylococcus aureus, a Gram-positive human commensal bacterium of the nasal epithelium turns virulent when the individual is immune-compromised
colony-forming unit (CFU) analysis and growth optical density (OD) demonstrated the non-antibacterial activity of thymol at 25, 50, and 100 μg/ml (Supplementary Figure S2A)
Thymol drastically inhibited the in vitro biofilm formation of S. aureus strains (MRSA American Type Culture Collection (ATCC) strain and clinical isolates) at 100 μg/ml without affecting the growth and the metabolic viability. This is more advantageous in excluding the possibility of drug resistance as thymol did not apply any selection pressure on methicillin-resistant S. aureus (MRSA)
Summary
Staphylococcus aureus, a Gram-positive human commensal bacterium of the nasal epithelium turns virulent when the individual is immune-compromised. S. aureus not alone causes simple skin infections and causes lethal infections such as pulmonary infections, invasive endocarditis, septic arthritis, osteomyelitis, and peri-implantitis (Taylor and Unakal, 2020). The treatment of these lethal conditions is a challenging task due to evolving multi-drug-resistant strains such as methicillin-resistant S. aureus (MRSA). Bacterial cells especially living in biofilm mode are having a peculiar behavior of synchronized virulence gene expression, and many enzymes present in biofilm matrix are reported to cleave the antibiotics. The bacterial cells residing in biofilm are much more resistant to antibiotics than their planktonic counterparts (Olsen, 2015; Hall and Mah, 2017)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
