Screening Asclepias syriaca for Antimicrobial Activity

Abstract

Antibiotic resistance, as well as the evolution and spread of new strains of disease causing agents are of great concern to the global health community. The high cost of antibiotics has made it inevitable to search for cheaper sources of antimicrobials. There has been considerable interest in the use of plant materials as an alternative method of controlling pathogenic microorganisms.
 Asclepias syriaca is one of such plants that need to be investigated in view of its acclaimed medicinal uses. It has been reported to contain certain bioactive chemicals which could be antimicrobial in action. This work investigated Asclepias syriaca stem for antimicrobial activity. Cold water, Hot water and Methanolic extracts of Asclepias stem were prepared using standard methods. The extracts were used to carry out susceptibility test, determine minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) of the stem extract on Salmonella typhi, Salmonella typhimurium, and Pseudomonas aeruginosa. The extracts were found to be effective on the three test organisms, with the methanolic extract being most active, followed by hot water extract, then cold water extract. Inhibitory zone diameter ranged between15 to 26mm for Methanolic extract, 14 to 23mm for Hot water extract, and 12 to 20mm for Cold water extract. The extracts were most active on Pseudomonas aeruginosa, then Salmonella typhi, and lastly Salmonella typhimurium. The MIC of the extract on Salmonella typhimirium was 200mg/mL for both the Cold and Hot water extracts, but 100 mg/mL for methanolic extract. The MIC of the extract on Salmonella typhi was 12.50mg/mL for Methalonic extract and for both Cold and Hot water extracts. For Pseudomonas aeruginosa, the MIC was 3.125mg/mL for all the extracts, i.e Cold and Hot water extracts, as well as Methanolic extract. MIC of the standard antibiotic was 3.125mg/mL.
 The MBC result showed no inhibition by all the extracts on Salmonella typhimurium, even at 400 mg/mL. All the extracts had MBC at 400 mg/mL for Salmonella typhi. All the extracts had MBC at 200 mg/mL on Pseudomonas aeruginosa, while MBC of the standard control on all test bacteria was 6.25 mg/mL. From our results, it is evident that Asclepias syriaca stem extracts possesses antimicrobial property which can be exploited to treat Salmonella typhi infection as used traditionally, as well as infections caused by Pseudomonas aeruginosa.