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The aim of this study was to evaluate the antimicrobial potential of violacein (VIO) on Staphylococcus epidermidis biofilm. The minimum biofilm inhibition concentration (MBIC) and minimum biofilm eradication concentration (MBEC) were determined, as well as the effect of VIO exposure time on microbial viability in mature biofilm. Violacein showed good antibiofilm action, inhibiting biofilm formation and eradicating mature biofilm of S. epidermidis at concentrations of 20 µg.mL-1 and 160 µg.mL-1, respectively. At concentrations equal to MBEC and 2x MBEC, the biofilm was eradicated in 3 h and 2h30min of incubation, respectively.When evaluating VIO modulating effect on the action of clinically-used drugs (vancomycin, cefepime, ciprofloxacin and meropenem), especial synergism was observed in the violacein-ciprofloxacin association, it can completely erradicated the mature biofilm at the concentration of 1/2xMBEC and 1/4xMBEC, respectively. VIO shows good antimicrobial action on S. epidermidis biofilm and has the potential to synergistically modulate the activity of clinically-used antimicrobials.

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AIMS: Violacein (VIO), a bacterial pigment produced by Chromobacterium violaceum, was examined to evaluate the antichagasic activity and its action mechanism against Trypanosoma cruzi Y strain. METHODS AND RESULTS: Violacein was tested against the epimastigote, trypomastigote and amastigote forms of T. cruzi Y strain (benznidazole-resistant strain). VIO inhibited all T. cruzi developmental forms, including amastigotes, which is implicated in the burden of infection in the chronic phase of Chagas disease (CD). VIO induced cell death in T. cruzi through apoptosis, as determined by flow cytometry analyses with specific molecular probes and morphological alterations, such as involvement of reactive oxygen species and changes in mitochondrial membrane potential and cell shrinkage. CONCLUSION: The results suggest antichagasic activity of VIO against T. cruzi Y strain with apoptotic involvement. SIGNIFICANCE AND IMPACT OF THE STUDY: The treatment of CD has limited efficacy and side effects that restrict patient tolerability and compliance. The VIO molecule could be used as a model for therapeutic alternatives for this disease.

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RESUMO A espécie Ocimum gratissimum (Linn.), popularmente conhecida como alfavaca-cravo, é muito utilizada na medicina popular. A planta apresenta inúmeros compostos, sendo o eugenol o constituinte majoritário do seu óleo essencial e o provável responsável pela sua atividade antimicrobiana. O objetivo deste estudo foi determinar o potencial antifúngico e o possível mecanismo de ação do óleo essencial extraído das folhas de O. gratissimum L. (OEOg) sobre cepas-padrão de Candida. Para avaliação da atividade antimicrobiana foi determinada a Concentração Inibitória Mínima (CIM), o efeito do tempo de exposição, o efeito modulador na atividade de antifúngicos (ATF) de uso clínico e a ação do OEOg nas fases de crescimento exponencial e estacionário de leveduras do gênero Candida. O mecanismo de ação do OEOg foi verificado por captação do cristal violeta e avaliação da morfologia microbiana pela técnica de microcultivo. Também foi avaliada a toxicidade do OEOg sobre hemácias humanas. O OEOg apresentou boa atividade antifúngica sobre cepas de Candida, sendo capaz de reduzir a taxa de crescimento das cepas de Candida a partir de quatro horas de exposição, além de ter modulado positivamente a atividade do cetoconazol para C. tropicalis ATCC 13803 e reduzir o número de células viáveis em todas as fases de crescimento microbiano. O OEOg foi capaz de promover o aumento discreto da captação do cristal violeta e provocou alterações na micromorfologia das células de Candida spp., sugerindo que seu alvo de ação seja o envoltório celular. Observou-se baixa toxicidade do OEOg sobre hemácias humanas. Os resultados encontrados mostraram que o OEOg possui boa atividade sobre o gênero Candida, com mecanismo de ação mediado possivelmente pela ocorrência de danos no envoltório celular, além de ter sido observada baixa toxicidade, indicando do OEOg é promissor no desenvolvimento e elaboração de um novo fármaco com potencial atividade para o tratamento de doenças fúngicas.

ABSTRACT Ocimum gratissimum (Linn.) is a medicinal plant popularly known as “wild basil” widely used in traditional medicine. The plant has numerous compounds, and eugenol is the major constituent of its essential oil and likely responsible for its antimicrobial activity. The aim of this study was to determine the antifungal activity and the potential mechanism of action of the essential oil extracted from the leaves of O. gratissimum L. (OEOg) against standard strains of Candida. The following experiments were performed: determination of Minimum Inhibitory Concentration (MIC), determination of the effect of exposure time to OEOg; evaluation of the modulating effect of OEOg in antifungal (ATF) activity for clinical use; determination of the effects of the OEOg on different growth phases of Candida spp; determination of crystal violet (CV) uptake and the microculture of yeast technique. OEOg showed good antifungal activity against Candida, being able to reduce microbial growth during 24 hours of contact and also the number of viable cells at all stages of growth. OE positively modulates the activity of ketoconazole for C. tropicalis ATCC 13803. Increased uptake of CV and also the inhibition of Candidavirulence factors were also observed, which indicates the occurrence of damage in the cell envelope. These findings, coupled with the low toxicity of OEOg on human erythrocytes, indicate that “wild basil” is a promising plant for the development of a new drug with a potential activity to treat fungal diseases.

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