Thymol Inhibits Biofilm Formation, Eliminates Pre-Existing Biofilms, and Enhances Clearance of Methicillin-Resistant Staphylococcus aureus (MRSA) in a Mouse Peritoneal Implant Infection Model

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is a common human pathogen that causes several difficult-to-treat infections, including biofilm-associated infections. The biofilm-forming ability of S. aureus plays a pivotal role in its resistance to most currently available antibiotics, including vancomycin, which is the first-choice drug for treating MRSA infections. In this study, the ability of thymol (a monoterpenoid phenol isolated from plants) to inhibit biofilm formation and to eliminate mature biofilms, was assessed. We found that thymol could inhibit biofilm formation and remove mature biofilms by inhibiting the production of polysaccharide intracellular adhesin (PIA) and the release of extracellular DNA (eDNA). However, cotreatment with thymol and vancomycin was more effective at eliminating MRSA biofilms, in a mouse infection model, than monotherapy with vancomycin. Comparative histopathological analyses revealed that thymol reduced the pathological changes and inflammatory responses in the wounds. Assessments of white blood cell counts and serum TNF-α and IL-6 levels showed reduced inflammation and an increased immune response following treatment with thymol and vancomycin. These results indicate that combinatorial treatment with thymol and vancomycin has the potential to serve as a more effective therapy for MRSA biofilm-associated infections than vancomycin monotherapy.

Antimicrobial Wound Dressings against Fluorescent and Methicillin-Sensitive Intracellular Pathogenic Bacteria

“…These studies corroborate our results that not only 7 mg of PCL-THY eliminate already formed biofilms but also that the exposition to 5 mg PCL-THY for 24 h reduces bacterial attachment to the well. The obtained results may evidence that cell wall damage can negatively affect bacterial attachment as we previously described, which, according to Kerekes et al represents the first step in biofilm formation, followed by formation of microcolonies, maturation, and cell dispersal. ,, The effect of THY against bacterial adhesion has also been demonstrated by Yuan et al when they analyzed PIA (polysaccharide intracellular adhesion), a component involved in adhesion and aggregation. This component was reduced under the presence of THY, and thus, bacteria could adhere to materials at the initial stage, but they were unable to form biofilms due to a reduced cell-to-cell adhesion. , Therefore, THY reduces bacterial growth, interferes with biofilm formation, and promotes biofilm eradication …”

“…In this sense, Yuan et al also showed the efficiency of free THY in the inhibition of biofilm obtained from the non-clinical MRSA strain TCH1516 (ATCC BAA-1717). Biofilm formation and mature biofilm were inhibited by the treatment with up to 512 μg/mL of free THY, a concentration much higher than those released from our mats, though not achieving the complete eradication of bacteria growth . Moreover, Cabarkapa et al treated bacteria (Salmonella enteritidis) with sub-MIC (MIC/2-MIC/4) concentrations of Origanum and Thymus EOs as well as their active components carvacrol and THY, and results showed that biofilm formation was inhibited .…”

“…Biofilm formation and mature biofilm were inhibited by the treatment with up to 512 μg/mL of free THY, a concentration much higher than those released from our mats, though not achieving the complete eradication of bacteria growth. 54 as their active components carvacrol and THY, and results showed that biofilm formation was inhibited. 32 These studies corroborate our results that not only 7 mg of PCL-THY eliminate already formed biofilms but also that the exposition to 5 mg PCL-THY for 24 h reduces bacterial attachment to the well.…”

“…This component was reduced under the presence of THY, and thus, bacteria could adhere to materials at the initial stage, but they were unable to form biofilms due to a reduced cell-to-cell adhesion. 54,56 Therefore, THY reduces bacterial growth, interferes with biofilm formation, and promotes biofilm eradication. 32 3.4.…”

Common Plant-Derived Terpenoids Present Increased Anti-Biofilm Potential against Staphylococcus Bacteria Compared to a Quaternary Ammonium Biocide

“…In our study, biofilms were left to be formed for 48 h under static conditions, resulting in both species achieving biofilm populations of over 10 7 CFU/cm 2 by the end of incubation (just before disinfection; results not shown). Such cell-concentration levels are considered adequate for sufficient (mature) biofilm formation (and not just individual cells attachment), with many other previous studies having left staphylococci to form biofilms on PS microtiter plates for just 24 h before further experimentation [59][60][61]. However, we still do not have any other further info regarding the structure and composition of the extracellular material of the biofilms formed here or whether and in which way these characteristics, together with the variation in biofilm incubation time (or many other parameters that could potentially influence biofilm growth), could affect the resistance of the enclosed bacteria to the tested antimicrobials.…”