Perfil antimicrobiano e antioxidante de metabólitos produzidos por fungos filamentosos do bioma Caatinga

Abstract

The advent of antibiotics has been revolutionary in medical treatment, allowing the development of invasive and surgical techniques that have made it possible to recover and sustain human life after surgery, as well as to cure previously fatal infectious diseases. However, their excessive and irregular use, together with the genetic mechanisms developed by the microorganisms themselves, have led to the emergence of microbial resistance, a growing problem that has become a global concern in the 21st century, highlighting the need for research into new antimicrobial agents. In addition to antimicrobial activity, the search for new bioactive compounds derived from natural substances has great potential for application and use in the search for compounds with antioxidant activity, which is essential in combating the ageing of the human body and degenerative diseases. In this perspective, the search for filamentous fungi producers of bioactives from the Caatinga biome, an exclusively Brazilian biome, may be strategic, since this environment is characterised by unique climatic and environmental conditions and the endemic organisms may produce differentiated secondary metabolites. Thus, the aim of this study was to evaluate the antimicrobial and antioxidant potential of secondary metabolites produced by filamentous fungi from lichens of the Caatinga of Alagoas. For this objective, 35 fungi were selected and the production of secondary metabolites was performed by cultivation in Czapek solid agar medium for 15 days at 30.0 ºC, followed by extraction in ethyl acetate (C4H8O2) and evaluation of the yield. Antimicrobial activity was determined by disc diffusion method and microdilution in Sabouraud broth, and antioxidant inhibition potential was evaluated by 2,2-diphenyl-1- picrylhydrazyl (DPPH) radical and iron reducing power (FRAP) methods. Of the 35 fungi evaluated, four (11%) showed antimicrobial activity and six (17%) exhibited an antioxidant activity. The extract of Penicillium sp. 2UVC8, followed by Fusarium sp. 3UVLFC1, demonstrated the best activities against Staphylococcus aureus with minimum inhibitory concentrations (MIC) of 125 μg/mL and 250 μg/mL, respectively. The ethyl acetate, chloroform and hexane fractions of Fusarium sp. 3UVLFC1 extract revealed promising potential against S. aureus. In the evaluation of antifungal activity, the extract of Fusarium sp. 4UVLFC2 demonstrated MIC = 31.2 μg/mL, against C. albicans. However, neither extract showed any inhibitory effect on the gram-negative bacteria strains E. coli and P. aeruginosa. In the antioxidant determination, the extract of Fusarium sp. 4LCEM2 obtained promising results with CE50 = 180 μg/mL As far as the cytotoxic effect against human blood lymphocytes is concerned, the extracts of Fusarium sp. 3UVLFC1, Penicillium sp. 2UVC8 and Penicillium sp. 11LCL5 did not show any cytotoxicity even at high concentrations such as 2000 and 1000 μg/mL. Fourier transform infrared spectrometer (FTIR) analysis of the fungal extracts revealed quite complex signals. Others were very similar even among different genera. The results showed promising antibacterial activity against S. aureus and antioxidant potential without human lymphocyte cytotoxicity. These results emphasize the richness of the biodiversity of the Caatinga and the prospection of its microorganisms, which are sources of metabolites with a high biotechnological potential.