Aims The study aimed to assess whether violacein has antimicrobial activity on Staphylococcus epidermidis and synergistically modulates the action of commercially available antimicrobial drugs. Methods and Results Violacein showed excellent antimicrobial activity on biofilm‐forming and nonbiofilm‐forming S. epidermidis strains (ATCC 35984) (ATCC 12228), with bacteriostatic (MIC = 20 μg ml−1 and 10 μg ml−1 respectively) and bactericidal effects (MBC = 20 μg ml−1 for both strains), observed in short periods of exposure. The violacein bactericidal concentration led to S. epidermidis death after 2–3 h of exposure. Additionally, violacein synergistically modulated the activity of different antimicrobial classes on S. epidermidis ATCC 12228 (81·8%; n = 9) and on S. epidermidis ATCC 35984 (54·5%; n = 6), reducing the MIC of these antibiotics by up to 16‐fold. Conclusion Violacein shows excellent antimicrobial activity on S. epidermidis strains. Significance and Impact of the Study Violacein shows the potential for the development of a new drug for the treatment of infections caused by S. epidermidis.

Violacein is an indole compound, produced by Chromobacterium violaceum, a bacteria present in tropical and subtropical areas. Among its numerous biological activities, its antimicrobial potential stands out. This study aims to determine the antimicrobial activity of VIO on S. aureus in planktonic culture and biofilms. VIO showed excellent antimicrobial activity in inhibiting and killing S. aureus in planktonic cultures and biofilm formation. The minimum bactericidal concentration (5 μg/mL) of VIO caused the death of S. aureus after 3–4 h of exposure and the minimum inhibitory concentration (1.25 μg/mL) of VIO inhibited bacterial growth within the first 8 h of contact. Biofilm formation was also strongly inhibited by VIO (1.25 μg/mL), in contrast to the higher resistance verified for S. aureus in mature biofilm (40 μg/mL). The high bacterial metabolic activity favored VIO activity; however, the good activity observed during phases of reduced metabolism indicates that VIO action involves more than one mechanism. Thus, VIO is a promising molecule for the development of an antimicrobial drug for the eradication of S. aureus infections.

RESUMO:A espécie Ocimum gratissimum (Linn.), popularmente conhecida como alfavacacravo, 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. Palavras-chave:Ocimum, óleos essenciais, atividade antimicrobiana, farmacologia. ABSTRACT: Antifungal activity and potential action mechanisms of essential oil ofOcimum gratissimum (Linn.) leaves against Candida species. 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 microcultu...

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Introduction: Momordica charanthia L., Curcubitaceae, is a pantropical food and medicinal plant. The plant is included in the Official List of Brazilian Medicinal Plants of interest to the Brazilian Unified Health System. The study aimed to perfom microbiological studies with extracts of Momordica charanthia L. including chemical characterization of the active extracts. Methods: The antimicrobial activity was evaluated with the hydroalcoholic and acetone extracts of M. charantia leaves, fruits and seeds from northeastern Brazil using microdilution broth technique on the selected clinical bacterial and fungal strains. Extracts that presented antimicrobial were subjected to ultra performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QToF-ESI-MS). Results: The in vitro antimicrobial assays demonstrated that the leaves extracts presented good antibacterial effect against four Staphylococcus aureus strains, and a weak antifungal activity agaist Candida albicans. Fourteen compounds were identified in the hydroalcoholic extract, while 12 were found in the acetone extract. The most important compounds were kaempferol, quercertin and triterpenoids like cucurbitacins. Conclussion: The present study demonstrated the potential antibacterial activity of M. charantia L. from northeastern part of Brazil, in addition to important phytochemical metabolites known to possess antibacterial activities, particularly against microrganisms of clinical importance. The UPLC phytochemical profile of the Brazilian variety is reported here for the first time. The phytochemical profile of the LHE and FAE demonstrated the presence of biologically and pharmacologically active compounds. There is lack of biological and pharmacological studies to support the medicinal uses of this important plant. The Brazilian variety of M. Charantia could be a potential therapeutic agent in the treatment of infections.

Fungal diseases and the progressive development of resistance are a challenge. In this context, Lippia alba (lemon balm) is a species used in folk medicine, being described with antimicrobial potential. The aim of this study was to determine the antifungal activity and modulating effect of the essential oil of Lippia alba (Mill.) N.E. Brown leaves (LaEO). The antifungal activity of LaEO on eight Candida strains was determined by minimum inhibitory concentration (MIC) and minimum lethal concentration (MLC), minimum biofilm inhibition concentration (MBIC), minimum biofilm eradication concentration (MBEC) and time-kill. The checkerboard technique was used to determine the modulating effect of LaEO on antifungal activity. The results indicate the presence of 11 constituents, with a predominance of carvone (58.15%) and limonene (25.37%). LaEO was able to inhibit the growth of all tested microorganisms, with MIC and MLC ranging from 0.078 to 1.25 mg/mL and MBIC and MBEC ranging from 0.156 to 5 mg/mL. The time-kill assay showed that LaEO was able to eliminate the strains after two hours of exposure and the best association was observed for the combination of LaEO and ketoconazole. The results of the study indicate that LaEO has excellent antifungal activity with potential biotechnological application.