Antibacterial potency of mid-polar extracts obtained from Malaysian plant Parkia speciosa against human pathogenic bacteria

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Plants contain a wide variety of bioactive compounds, which have attracted the interest of researchers in finding novel sources of natural medicine. In the following paper, we aim to evaluate the antibacterial potential of extract fractions associated with Parkia speciosa pods and beans against human pathogenic bacteria. Antimicrobial activity was determined with disc diffusion and broth microdilution assays against eight skin colonising microorganisms including Staphylococcus aureus , Staphylococcus epidermidis , Salmonella enterica , Escherichia coli , Pseudomonas aeruginosa , Klebsiella pneumonia followed by further fractionation of the pods ethyl acetate fraction by column chromatography along with preparative thin-layer chromatography. Quantification of bacterial death mechanism was elucidated by the measurement of hole size in cell wall that has been induced by extract constituents via field-emission scanning electron microscopy (FESEM). Four fractions showed significant antimicrobial activity against the six microorganisms tested (p < 0.01), with inhibition zones ranging from 35.67 to 17.00 mm, and minimum inhibitory concentration ranging from 6.25 to 50.00 mg/ml in which the pods ethyl acetate fraction was the most effective. The methanol fraction isolated from the pods ethyl acetate fraction was much more effective with a four-fold increase from 6.25 to 1.25 mg/ml against S. epidermidis. The disintegration of S. aureus was due to chronic cell wall alterations with pore creation, invaginations and morphological disorganisation. Autolysis in bacterial cells via the expression of peptidoglycan-disrupting lysozyme or bacterial murein hydrolase was postulated. A significantly large pore with a mean diameter of 293.7 nm was detected in the cell wall of S. aureus . P. speciosa fraction could be a potential novel source for the development of a natural antibacterial agent. • Four fractions of Parkia speciosa showed significant antimicrobial activity against the six microorganisms tested. • Pods ethyl acetate fraction was the most effective. • The methanol fraction isolated from the pods ethyl acetate fraction was much more effective with a four-fold increase from 6.25 to 1.25 mg/ml against S. epidermidis. • The disintegration of S. aureus was due to chronic cell wall alterations with pore creation, invaginations and morphological disorganisation. • Autolysis in bacterial cells via the expression of peptidoglycan-disrupting lysozyme or bacterial murein hydrolase was postulated.

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