A Convenient Microdilution Method for Screening Natural Products Against Bacteria and Fungi

Abstract

Candida albicans, Cryptococcus neoformans, Mycobacterium tuberculosis, Pseudomonas aeruginosa, and Staphylococcus aureus (methicillin-susceptible and -resistant strains) are some of the most common pathogens of immunocompromised individuals. Since multi-drug resistance of these microorganisms is a major medical problem, we propose a convenient microdilution method for screening of natural products in a search for new antimicrobial agents that would be active against these organisms. To enable the screening process under standard laboratory conditions, Cr. albidus and M. smegmatis were used as model-organisms in place of their pathogenic counterparts. Antibiotics were used as positive controls, and their MIC values were in agreement with the MIC ranges recommended by the National Committee for Clinical Laboratory Standards. Organic plant extracts from Lemna minor and Ilex cornuta were used for developing the microdilution assay. The method can be used as a reliable tool for discovering antimicrobial agents with novel chemistry. It is adopted for organic extracts at a microgram scale and is currently being used for screens of more than one thousand extracts from the National Cancer Institute Open Repository.

Comparação de métodos para avaliação da atividade antimicrobiana e determinação da concentração inibitória mínima (cim) de extratos vegetais aquosos e etanólicos

“…A confirmação da presença de células vivas com o uso do CTT ou a presença de células viáveis em ágar exclui a necessidade da utilização de outros testes em base ágar. Zgoda;Porter (2001) avaliaram extratos orgânicos das plantas Lemma minor L. e Ilex cornuta Lindl. pela metodologia de microdiluição em caldo e afirmaram que esse método se mostrou confiável para a triagem de produtos naturais contra bactérias e fungos, permitindo realizar triagem antimicrobiana e determinando a CIM em testes com um grande número de extratos, pela utilização de uma escala de nanogramas a microgramas dos compostos a serem testados.…”

Phytochemical and Antibacterial Evaluations of the Stem Bark of <i>Newbouldia laevis</i> against Isolates from Infected Wounds and Eyes

“…The modified method of [17] was employed to determine the MIC of the extract (MSE) and its aqueous fraction. Serial two-fold dilutions of 2ml each were made in a concentration range of 50 to 0.391 mg/ml of the extract and 25 to 1.5625 mg/ml of the aqueous fraction using double strength nutrient broth supplemented with 10 % glucose.…”

Screening of antimicrobial activity of essential oil and methanol extract of Satureja hortensis on foodborne bacteria and fungi

“…The essential oils and extracts of Satureja hortensis, dissolved in 10% dimethylsulfoxide (DMSO), were first diluted to the highest concentration (500 µg/ml) to be tested, and then serial two-fold dilutions were made in order to obtain the concentration range from 7.8 to 500 µg/ml in 10 ml sterile test tubes containing nutrient broth. MIC values of Satureja hortensis extracts against bacterial strains and Candida albicans isolates were determined, based on a micro-well dilution method (Zgoda & Porter 2001;Gulluce et al 2004a) with some modifications.…”