In vitro Antimicrobial Activity of Some Medicinal Plants Found in Saudi Arabia

The methanolic extracts of Citrullus colocynthis, Rhazya stricta, Datura stramonium and Zygophyllum coccineum were evaluated for the antimicrobial activity against Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25928, Streptococcus pyogenes grp A (clinical isolate), Bacillus subtilis ATCC 6633 and Candida albicans ATCC 10231. The extract of different plants tested showed varying degree of inhibitory activity against the tested pathogens. Extract of C. colocynthis showed the highest activity followed by R. stricta, while Z. coccineum exhibited least activity. The gram positive bacteria were observed to be more sensitive to plant extracts as compare to gram negative bacteria. Moreover, all extract were effective against C. albicans. While, only the extract of C. colocynthis was able to inhibit the growth of P. aeruginosa (18.3 mm). The maximum zone of inhibition was observed against S. aureus (31.3mm) by the extract of C. colocynthis and the MIC against the same bacteria was 0.2 mg/ml. The GCMS analysis of C. colocynthis extract showed the presence of several esters, glycosides, alkaloids and flavonoids. However, the main component detected in the extract was l-(+)-Ascorbic acid 2,6-dihexadecanoate; a known hyaluronidase inhibitor. Therefore, the results showed that C. colocynthis possesses a broad spectrum of activity against pathogenic bacteria responsible for the most common microbial diseases.