Abstract
The high resistance of staphylococcal biofilm against antibiotics and developing resistance against antiseptics induces a search for novel antimicrobial compounds. Due to acknowledged and/or alleged antimicrobial activity of EOs, their application seems to be a promising direction to follow. Nevertheless, the high complexity of EOs composition and differences in laboratory protocols of the antimicrobial activity assessment hinders the exact estimation of EOs effectiveness. To overcome these disadvantages, in the present work we analysed the effectiveness of volatile and liquid forms of seven EOs (derived from thyme, tea tree, basil, rosemary, eucalyptus, lavender, and menthol mint) against 16 staphylococcal biofilm-forming strains using cohesive set of in vitro techniques, including gas chromatography–mass spectrometry, inverted Petri dish, modified disk-diffusion assay, microdilution techniques, antibiofilm dressing activity measurement, AntiBioVol protocol, fluorescence/confocal microscopy, and dynamic light scattering. Depending on the requirements of the technique, EOs were applied in emulsified or non-emulsified form. The obtained results revealed that application of different in vitro techniques allows us to get a comprehensive set of data and to gain insight into the analysed phenomena. In the course of our investigation, liquid and volatile fractions of thyme EO displayed the highest antibiofilm activity. Liquid fractions of rosemary oil were the second most active against S. aureus. Vapour phases of tea tree and lavender oils exhibited the weakest anti-staphylococcal activity. The size of emulsified droplets was the lowest for T-EO and the highest for L-EO. Bearing in mind the limitations of the in vitro study, results from presented analysis may be of pivotal meaning for the potential application of thymol as a antimicrobial agent used to fight against staphylococcal biofilm-based infections.
Highlights
Biofilm is a cohesive and complex community consisting of microbial cells, embedded within a self-produced matrix that displays protective and nutritional features
The results of numerous studies indicate that Essential oils (EO) are a promising alternative to antibiotics thanks to their broad spectrum of antimicrobial activity and unspecific mode of action, which correlates with low risk of microbial resistance emergence [19,20]
It is reported that EOs may exhibit such other mechanisms of action against biofilms as blocking the quorum-sense system, inhibiting the transcription of flagellar genes, interfering with bacterial motility, reducing the bacterial adherence to inert surfaces, increasing the oxidative stress in microbial cells, and blocking the productions of enzymes [22]
Summary
Biofilm is a cohesive and complex community consisting of microbial cells, embedded within a self-produced matrix that displays protective and nutritional features. Bacteria within the biofilm, compared to their planktonic (non-aggregated) counterparts, demonstrate specific patterns of growth rate, gene transcription, and metabolic activity. It translates into (among others) highly elevated biofilm tolerance/resistance to environmental stress and eradication with antimicrobials [1]. Biofilm is a significant causative factor in a number of persistent, hard-to-heal infections, including these occurring in chronic wounds and bones [2]. Due to biofilm’s persistence, even systemic high-dose antibiotic therapy displays low efficacy; in turn, topical application of antibiotics to treat biofilm-based infections is associated with numerous adverse effects. The treatment of biofilm-based, chronic bone and wound infections requires (if possible) surgical intervention and application of antiseptics [3]. As numerous reports indicate microbial resistance to antibiotics and to antiseptics, a growing interest in new antimicrobials and novel ways of their administration is presently observed [4]
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