Abstract
This study was aimed exploring the cytotoxicity and antimicrobial activity of the leaves D. thwaites is an endemic plant to Sri Lanka. The plant is known for its nutritional and medicinal applications where especially the leaf decoctions are being used to wash skin wounds in indigenous medicine. The brine shrimp lethality assays was performed to evaluate normal toxicity and it gave LC50 value greater than 1000 μg/ mL showing that the plant extracts are non-toxic to the normal cells. The agar-well diffusion assay was performed to assess the antimicrobial activity, and strains of bacteria; E. coli, Staphylococcus aureus, Pseudomonas aeruginosa and Methicillin Resistant Staphylococcus aureus (MRSA) and fungus; Candida albicans were used as test organisms. The results indicated that all the extracts are active against Staphylococcus aureus (Gram Positive) with maximum inhibition shown for methanolic and aqueous extracts. When it was tested against MRSA both aqueous and methanolic extracts gave similar inhibitions. The minimal inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined as 6.25 mg/mL and 100 mg/mL respectively with S. aureus whereas no inhibition observed by any of the extract against Gram negative bacteria and Candida albicans. Thus, this study revealed the leaves of D. thwaites possesses strong anti-bacterial activity against S. aureus and MRSA. The results confirmed the efficacy of using D. thwaites as the natural antimicrobial agent and suggested to develop the leaves into value added products to be used in topical applications as antiseptic solutions or ointments.
 Asian J. Med. Biol. Res. June 2020, 6(2): 316-320
Highlights
The antibiotic resistance (ABR), multidrug resistant (MDR) strain in pathogenic bacteria and the evolution of new strains of disease causing agents, are of great concern to the global health community (Manandha et al, 2019; Giamarellou, 2010)
Results of MIC and minimum bactericidal concentration (MBC) determination The effectiveness of the extracts in tested bacterial strains was determined by measuring the minimum inhibitory concentration (MIC) which was done by lowering the concentration of anti-bacterial agent/ plant extract on inhibition of bacterial growth
MIC was performed for only the organisms, S. aureus, which showed a zone of highest inhibition with aqueous and methanolic extracts of leaves in the antimicrobial assay by agar well diffusion method
Summary
The antibiotic resistance (ABR), multidrug resistant (MDR) strain in pathogenic bacteria and the evolution of new strains of disease causing agents, are of great concern to the global health community (Manandha et al, 2019; Giamarellou, 2010). The pathological situation named “impetigo” is a common bacterial skin infection usually observed on the superficial epidermis and caused by Staphylococcus aureus. This infection accounts for 50% to 60% of all bacterial skin infections and topical antibiotic creams such as mupirocin and fusidic acid are prescribed as the treatments (Green et al, 2012). As a solution to penicillin resistance, a semi-synthetic penicillinase resistant penicillin called methicillin had been introduced but shortly Staphylococcus aureus has begun to develop methicillin resistance too (Breyre and Frazee, 2018) This methicillin resistant Staphylococcus aureus (MRSA) has been reported to cause many complications and difficult-to-treat diseases including abscess, purulent cellulitis and even severe skin and soft tissue infections (SSTI) (Kasote et al, 2015) while the number of efficient antibiotics against them are challenging.
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