Methods for in vitro evaluating antimicrobial activity of medicinal plants: the need for standardization

Abstract

The increasing incidence of resistant pathogens to current drugs encourages the search for new antimicrobial agents. In this context, medicinal plants are an important source of new drugs. There are several methods for evaluating the
antibacterial and antifungal activity of extracts, fractions, essential oils and isolated substances from the plant. The most known include diffusion, dilution and bioautography methods. The purpose of this paper is to present the most
used methods currently, along with their advantages, disadvantages and interfering factors. Among the works available in the SciELO database, covering the last ten years, only 4,4% of research on medicinal plants are related to the
antimicrobial activity. The most used method is microdilution (57,9%), the best recommended due to high sensitivity, the minimum quantity of reagents and sample and the possibility of a more significant number of replicates. In articles
that used this method, differences were observed in factors that may affect the results. Thereby, there is the need for standardization of methods used by researchers to facilitate obtaining comparable and reproducible results. To
achieve comparable and reproducible results, there is the need to standardize the methods used by the researchers. It is recommended to use as reference the standards established by CLSI for culture medium and inoculum concentration in
the tests. It also recommended the inclusion of negative control of the solubilization of the samples with quantification of microbial growth to avoid interference with the results.