Effect ethyl acetate extract of Lasiodiplodia pseudotheobromae IBRL OS-64 on growth and cell morphology of a foodborne bacterium, Bacillus cereus;(TJPS-2021-0112.R1)

Abstract

This study was undertaken to evaluate the effect of ethyl acetate extract of endophytic fungus, Lasiodiplodia pseudotheobromae IBRL OS-64 towards a test bacterium, B. cereus with emphasis on bacterial growth reduction and cell morphological changes. The ethyl acetate and methanolic extracts were screened for their antibacterial activity against test bacteria via agar disc diffusion assay. The results demonstrated that there is a significant antibacterial activity of the ethyl acetate extract with a diameter zone of inhibition in the value of 22.0 ± 0.6 mm. In broth microdilution assay, the MIC and MBC values of the extract were 250 and 500 µg/mL, respectively. The results revealed that the extract exhibited a bactericidal effect on the test bacterium. A time-kill study showed the antibacterial activity of the extract was dose and time-dependent. The morphological changes of the bacterial cells exposed to the extract were observed under a scanning electron microscope (SEM) and transmission electron microscope (TEM). The results revealed the abnormalities of the treated bacterial cells compared to the control and thus led to ultimate death beyond repair. The present study suggested the potency of the ethyl acetate extract of L. pseudotheobromae IBRL OS-64 could be further used as an antibacterial agent.