Time-kill kinetics and mechanism of action of Caesalpinia sappan L. and Ochna integerrima (Lour.) Merr. water extracts against pathogenic bacteria

Abstract

Context: Caesalpinia sappan and Ochna integerrima are two native plants of Thailand and distributed widely throughout the country. Recently, water extracts from the stem bark of C. sappan and O. integerrima were found to exhibit potently antibacterial property but the antibacterial mechanism of action toward target bacteria has not been investigated yet. Aims: To study time-kill kinetic and the mechanism of action of C. sappan and O. integerrima waterextracts toward target bacteria. Methods: The time-kill kinetic study of bacteriostatic or bactericidal activity against Gram-positive and Gram-negative pathogenic bacteria within 24 h experiment was conducted and the mechanism of action on cell morphology of the target bacteria by using scanning electron microscopy (SEM) were investigated. Results: Both of the C. sappan and O. integerrima water extracts possessed bacteriostatic or bactericidal activity toward six tested pathogenic bacteria. The bacteriostatic or bactericidal activity depending on bacterial strains and the test concentrations (0.5, 1 and 2 × MIC) of these two extracts to the tested bacteria were observed. The bactericidal activity against all of the tested bacterial was evinced at 2 × MIC. The morphological alterations of the target bacterial cells of changing the cell size (decreased and increased), cell lysis and having cell cavity were detected by SEM after the treatment with C. sappan and O. integerrima water extracts. Conclusions: The water extracts from the stem bark of C. sappan and O. integerrima exhibited bactericidal activity by changing the cell size, cell lysis and cell cavity of the tested bacteria cell morphology.