Activities of compound G2 isolated from alfalfa roots against dermatophytes

Abstract

An antimycotic agent, compound G2, isolated from alfalfa roots exhibited considerable activity against the six most common dermatophytes. MICs in agar and broth dilutions ranged from 10 to 30 ,ug/ml and from 2 to 10 ,ug/mIl, respectively. G2 was fungicidal at 5 to 22 ,ug/ml. Structure and toxicity relations are discussed.The widespread occurrence of skin, nail, and hair infections caused by dermatophytes, coupled with the limited number of available drugs effective against them, has led to a search for new antimycotic agents.A recently isolated compound, 02, which was extracted from the roots of alfalfa plants, showed considerable activity against plant pathogenic fungi (6) and medically important yeasts (8,9). Compound G2 was identified as the gluco derivative of medicagenic acid (MA), the major occurring saponin aglycon of alfalfa roots (1). It has been suggested that the antimycotic activity of compound G2 is related to the ability of alfalfa saponins to complex with sterols and that fungi susceptible to these compounds contain relatively higher proportions of sterols in their membranes (1). Numerous crude saponin extracts from other plants have also been shown to possess ant'imycotic activity (3, 4).The present study describes the fungicidal effect of compound 'G2, which was found to' be superior to all other chemically related compounds (listed below) against the six most common dermatophytes.Dermatophytes 'were isolated from clinical specimens taken from various body sites of patients. Dermatophyte isolates were identified by conventional methods (11) We also modified the method of susceptibility testing by broth dilution (12). Dermatophyte suspensions were prepared as described above. A 10-,il bacteriological loop of suspension was transferred to potato dextrose broth and incubated at 26°C. After 5 to 7 days, the mycelium was homogenized and filtered, and counting was done as described above. The tests were performed in test tubes containing different concentrations of G2 (between 5 and 30 ,ug/ml) and inocula of 105 particles in 4 ml of potato dextrose broth.Two inoculated tubes containing drug-free medium were included in each experiment. Three glass beads were added to each tube to enhance mixing. All tubes were incubated loosely capped at 30°C in a shaker.Susceptibility was esti'mated after 5 to 7 days of growth by determining the MIC as the lowest drug concentration at which the broth remained clear.The minimum fungicidal concentration was determined by assaying the CFU on PDA plates. Three 50-,u samples obtained immediately after vortex mixing from the tubes showing no growth were subcultured on PDA. The minimum fungicidal concentration was established as the lowest concentration of drug with which all subcultures were absolutely negative (exceeding the 99.9% killing endpoint).The antifungal effect of compound G2 was tested on numerous isolates of six species of dermatophytes by the agar and broth dilution method's. This provided in vitro assessment of both the MICs and minimum fungicidal concentrat...

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