Assessment of killing kinetics assay and bactericidal mechanism of crude methanolic bark extract of Casuarina equisetifolia.

Casuarina equisetifolia L. is an important medicinal plant widely used to treat various diseases particularly ulcers, diabetes, cough, diarrhea and many infectious and skin diseases. The aim of this research study was to examine the killing mechanism and killing kinetics assay of methanolic bark extract of C. equisetifolia against some highly resistant human pathogens. The comparison on antibacterial activity of extract was firstly done with six different well reputed antibiotics using disk diffusion method. The broth dilution method was used to measure the MIC and MBC values. The mechanism of killing was identified by scanning electron microscopy (SEM) technique. Results showed that higher inhibitory zones were produced by methanolic plant extract than that of some tested antibiotics. The lower MIC and MBC values indicated the antibacterial potency of plant extract. The extract of C. equisetifolia produced a more drop in optical density of S. aureus, MRSA B. subtilis and S. epidermidis up to 12 hrs. The complete destruction of the cell membrane of MRSA was observed after 12 h treatment with plant extract. It is concluded that crude bark extract of C. equisetifolia is potent antimicrobial agent and produced both bacteriostatic and bactericidal effects. Its killing time was extremely faster especially against MRSA. The cell membrane rapturing is a suggested killing mechanism of plant extract.