A proper use of medicinal plants requires accurate scientific information and understanding of their chemical constituents. The therapeutic effects in the plants are due to the chemical compounds therein. Cynodon dactylon (L.) Pers. of the family Poaceae is a perennial, pan-tropical species of grass which is a well-known traditional medicine and has a renowned position for treatment of many symptoms and diseases. The chemical composition, free radical scavenging activity, and antimicrobial properties of the methanolic extract of C. dactylon rhizomes against selected bacterial and fungal strains were investigated using disk-diffusion method. The results indicated that the major fatty acid structures of C. dactylon methanolic extract were palmitic acid (36.40%), oleic acid (28.26%), and linoleic acid (17.01%). Alpha-tocopherol (151.39 mg·kg−1) and sitosterol (3199.62 mg·kg−1) were the main tocopherols and sterols, respectively. According to the instrumental analysis, the total phenolic compounds of methanolic extract were equal to 917.08 mg·kg−1 and the main compound was hydroquinone (66.89%). Antioxidant activity of the methanolic extract at concentrations of 100–1000 ppm was 9.81–67.87%, which is significantly different from the 200 ppm synthetic antioxidant (BHT) with free radical scavenging activity equal to 48.93% (p<0.05). The antimicrobial study revealed that the methanolic extract of C. dactylon rhizomes was effective against all of the bacterial pathogens and the antibacterial activity increased with an increase in the concentration of extract. Therefore, the largest zone of inhibition was observed against Bacillus cereus (18.3 ± 0.4 mm) and Escherichia coli (16.8 ± 0.5 mm) at 1000 ppm. The highest resistance was observed with Pseudomonas aeruginosa (inhibition zone of 12.8 ± 0.15 mm). Methanolic extract at 200 ppm had no effect against fungus Aspergillus niger. However, at 1000 ppm concentration, an inhibition zone with a diameter of 14.4 ± 0.45 mm was formed.

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