Synergistic antibacterial activity of monoterpenes in combination with conventional antimicrobials against Gram-positive and Gram-negative bacteria / Atividade antibacteriana sinérgica de monoterpenos combinados com antimicrobianos convencionais frente a bactérias Gram-positivas e Gram-negativas

Introduction: bacterial infections are a public health problem. Besides, the emergence of strains resistant to antimicrobials has contributed to the search for new alternatives, such for the terpenes with antimicrobial potential. Objectives: the objective of this study was to determine the possible interaction of isolated monoterpenes (-)-Carveol, Geraniol, Citronellol, α-terpineol, R-(-) Carvone, (-)-Menthol, Linalool, D-Dihydrocarvone, and (-)-Terpine-4-ol with conventional antimicrobials (Chloramphenicol, Minocycline, Amoxicillin and Ciprofloxacin) when they are evaluated on Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa strains. Methodology: the minimum inhibitory concentrations of these test drugs were determined using the microdilution method. The Checkerboard method was used to assess the interactions, by determining the fractional inhibitory concentration index (FIC index). Results: aamong the monoterpenes, only Carveol, Citronellol, and Geraniol presented antimicrobial activity (MIC < 1024 µg/mL). They presented synergistic effects against Pseudomonas aeruginosa ATCC-9027 (FIC index ≤ 0.5) when in combination with Minocycline. Conclusion: this study contributes to the development of new approaches to control bacterial resistance and to the possibility of discovering new drugs.

Introdução: as infecções bacterianas são um problema de saúde pública. Além disso, o surgimento de cepas resistentes aos antimicrobianos tem contribuído para a busca de novas alternativas, como a pesquisa de terpenos com potencial antimicrobiano. Objetivos: o objetivo deste estudo foi determinar a possível interação de monoterpenos isolados (-) - Carveol, Geraniol, Citronelol, α-terpineol, R - (-) Carvona, (-)-Mentol, Linalol, D-Diidrocarvona e (-)-Terpina-4-ol com antimicrobianos convencionais (cloranfenicol, minociclina, amoxicilina e ciprofloxacina) quando avaliados em Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis, Escherichia coli e Pseudomonas aeruginosa. Metodologia: as concentrações inibitórias mínimas destas drogas foram determinadas usando o método de microdiluição. O método checkerboard foi utilizado para avaliar as interações, determinando o índice de concentração inibitória fracionária (índice FIC). Resultados: entre os monoterpenos, apenas Carveol, Citronelol e Geraniol apresentaram atividade antimicrobiana (CIM < 1024 µg/mL). Eles apresentaram efeitos sinérgicos contra Pseudomonas aeruginosa ATCC-9027 (índice FIC ≤ 0,5) quando em combinação com Minociclina. Conclusão: este estudo contribui para o desenvolvimento de novas abordagens para o controle da resistência bacteriana e para a possibilidade de descoberta de novas drogas.

Antifungal activity study of the monoterpene thymol against Cryptococcus neoformans.

Cryptococcus neoformans is a yeast fungus, which causes cryptococcosis, triggered by basidiospore inhalation and consequent dissemination to the central nervous system. In this study, we analyzed the antifungal action of thymol against 10 clinical strains of C. neoformans and analyzed the interaction of this monoterpene with sterols. The MICs of thymol ranged from 20 to 51 µg/ml, while the MFC values varied between 40 and 101 µg/ml. For the strains ICB-2601 and LM-39, in the presence of ergosterol, the MIC of thymol was 64 µg/ml, and in the presence of cholesterol, its MIC was 32 µg/ml. Based on the results, thymol presents antifungal action and seems to interact with ergosterol, but not with cholesterol. Complementary studies are needed to analyze its full effects.