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Objective:To test the in vitro antimicrobial efficacy of water and methanol extracts of 23 plan species that are commonly used in Libyan folk medicine.Methods:The antimicrobial activity was determinec using the well-diffusion method.Four test microorganisms were used namely,Escherichia coli,Salmonella species,Staphylococcus aureus and Bacillus subtilis.The minimum inhibitory concentration(MIC) was determined for the high biologically active crude plant extracts.Results:Among 23 medicinal plants used in the study,only 5 methanolic extracts[Rosmarinus offcinalis L,Carduus marianium L.,Lantana camara L.,Rhus tripartite(ueria) Grande,and Thymus capitatus(L.) Hoffm(link)]showed the highest antimicrobial activity againsl Staphylococcus aureus,Bacillus subtilis and Salmonella species,while 22 methanolic and aqueous extracts showed moderate to weak antimicrobial activity on all tested organisms.However 19 of the extracts showed no activity at all against Gram-ve and Gram +ve microorganisms.MIC was found to be 1.25 mg/mL(Thymus capitatus),3 mg/mL(Rhus tripartite),4 mg/mL(Carduus marianium),5 mg/mL(Rosamarinus officinalis) and5 mg/mL(Lantana camara),respectively.Conclnsions:The present results revealed that,crude methanolic extracts of the investigated Libyan folk medicinal plants exhibited mild to high in vitro antibacterial activities against Gram-positive and Gram-negative microorganisms.