Time-kill study and morphological changes of Proteus mirabilis cells exposed to ethyl acetate crude extract of Lasiodiplodia pseudotheobromae IBRL OS-64

ABSTRACT

@#Aims: To investigate time-kill curve and morphological changes of Proteus mirabilis cells exposed to ethyl acetate crude extract of endophytic fungus, Lasiodiplodia pseudotheobromae IBRL OS-64, isolated from Ocimum sanctum. Methodology and results: Inhibitory effect of the fungal extract against the test bacteria via disc diffusion assay showed a fair antibacterial activity with diameter of inhibition zone was 12.0 ± 0.4 mm. The Minimal Inhibition Concentration (MIC) and Minimal Bactericidal Concentration (MBC) values of the ethyl acetate extract against P. mirabilis was 250 and 500 µg/mL, respectively. The value of MBC which is two-fold higher than MIC value indicated that the fungal extract exerted bactericidal effect on bacterial cells of P. mirabilis. Time-kill curve study revealed that the bactericidal effect of the crude extract towards test bacteria was both dose and time dependent. Scanning electron microscope (SEM) observation revealed that the bacterial cells of P. mirabilis exposed to fungal crude extract resulted in formation of pits, irregular shape of the bacterial cell and ultimately cell death beyond repair. Conclusion, significance and impact of the study The time-kill curve study, and cell morphological changes suggested the potential of ethyl acetate extract of L. pseudotheobromae IBRL OS-64 against P. mirabilis infection by formation of cavities, irregular bacterial cell that leads to ultimate cell death and the extract may have pharmaceutical potential to be develop as antibacterial agent.