| Summary: | Signalling molecules are extensively studied in recent years because of their potential to control pathogens. Microorganisms naturally produce quorum sensing molecules (QS) as a tool for intra- and inter-species communication. Farnesol is synthesized as a by product of the ergosterol pathway of the yeast Candida albicans and in a concentration dependent maner blocks the morphological shift from the yeast to the hyphal form. The aim of this work was to study the effect of farnesol (30-300 microM) and the combination of farnesol with antibiotics (oxacillin, ciprofloxacin) on mixed biofilms formed by C. albicans/ S. aureus. For this purpose, clinical strains of S. aureus from blood cultures and central venous cathethers were collected. Overall, 8 MRSA and 3 MSSA were identified by PCR by detection of FemA, MecA genes. Strains were characterized according to selected virulence factors associated with resistance to antibiotics and disinfectants or biofilm formation (Nor, Qac genes coding for efflux pumps, Ica operon). The efficacy of farnesol to single and mixed biofilms was determined using different approaches, the total biomass stainning (crystal violet), metabolic activity meassuring (MTT test), colony forming units counting (CFU/ml) and microscopy (SEM). The concentration of 300 microMwas determined as the MIC50 of farnesol inhibiting mixed biofilm formation. This concentration did not show mutagenic potential according to the Ames test and was not cytotoxic for HeLa cell line. SEM definitely confirmed that farnesol inhibited hyphae of C. albicans that are a suitable substrate for adherence of staphilococci. Testing a combination of farnesol with oxacillin by E-test revealed an enhancing susceptibility of MRSA and MSSA to oxacillin. This effect was already observed and it can be associated with the inhibition of cell wall biosynthesis through the reduction of free C55 lipid carrier with subsequent retardation of murein monomer precursor transport across the cell membrane. We can conclude, that farnesol has multiple effects on mixed biofilms.
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