INFLUENCE OF A QUORUM SENSING COMPOUND ON Rhodotorula mucilaginosa PLANKTONIC CELLS

Yeasts generally live in complex environments, that they share with numerous other microbial organisms. In order to survive, they need to organize themselves in relation to behavior on a population basis. This is commonly mediated by small segregated molecules that accumulate depending on cell density, and upon reaching a threshold, influence cellular behavior, a mechanism called quorum sensing (QS), that is a form of molecular communication between microbial communities. The QS is widely studied in bacterial and fungal species, where this system is responsible for regulating important virulence factors, being possible the discovery of an essential molecule to the system, farnesol. Rhodotorula spp. are common yeasts in the environment, but in the last decades the number of human infections by this agent has increased, mainly in immunocompromised patients. It is important to point out that yeasts belonging to this genus present a high level of resistance to the antifungal agents of the azole and echinocandin classes. Therefore, the aim of this study was to evaluate the activity of farnesol against Rhodotorula mucilaginosa isolates in their planktonic form. Two clinical isolates of R. mucilaginosa from the Micoteca of the Laboratory of Medical Mycology, Laboratory of Teaching and Research of Clinical Analyzes (LEPAC / UEM) and one ATCC 64684 (R. mucilaginosa) were tested. Candida albicans ATCC 90028 was used as control. The farnesol (Sigma-aldrich) activity in planktonic cells was assessed by the minimal inhibitory concentration (MIC) according to CLSI M27-A3 method, using a range of concentration that varies from 0.2 to 2.1 µg/ml. The mitochondrial activity was measured by reduction of tetrazolium salts (XTT). The minimum concentration that presented the greatest action in reducing the metabolic activity for both isolates of R. mucilaginosa was 0.9 µg/ml, reducing in 80% for the standard stream and 61% for the clinical isolates. While for C. albicans, the minimum concentration that reduce the metabolic activity was 0.7 µg/ml, showing a reduction of only 32%. It has already known, that in C. albicans, farnesol acts by promotes reverse morphogenesis. Therefore, our results suggest farnesol may also act synergistically with conventional antifungal agents, especially on clinical isolates that are resistant to antifungal agents. However, to our knowledge, this is the first study about the influence of this compound on R. mucilaginosa planktonic cells, further studies are still needed to elucidate this effect.