Streptococcus mutans and S. agalactiae have been reported in human oral diseases including caries and periodontitis. Thus, present study was performed to investigate the effect of ethyl acetate crude extract of Lasiodiplodia pseudotheobromae IBRL OS-64, an endophytic fungus isolated from Ocimum sanctum leaf against S. mutans and S. agalactiae. Disc diffusion and broth microdilution assays were used to determine the antimicrobial activities with minimum inhibitory concentration and minimum bactericidal concentration values. Meanwhile, Microscopic analysis was used to study structural degeneration of bacterial cells. The fungal crude extracts demonstrated favorable antibacterial activity towards both test bacteria and produced inhibition zone ranging from 16 21.2 mm. The MIC and MBC values of the fungal crude extract towards S. mutans and S. agalactiae were determined and the results showed that the MIC and MBC values were in the range of 125-500 µg/ml and 125-1000 µg/ml, respectively. The time-kill study suggested that the ethyl acetate crude extract possessed bactericidal effect with concentration and time dependent. Structural degeneration studies revealed the major abnormalities occurred to S. mutans cells after treated with the fungal crude extract where completed alterations of their morphology with formation of cavities and collapsed cells beyond repair occurred. Therefore, the current study suggested the ethyl acetate crude extract of L. pseudotheobromae IBRL OS-64 could be an effective antibacterial agent to treat oral cavity bacteria.
Key words: Streptococcus mutans, Streptococcus agalactiae, Lasiodiplodia pseudotheobromae, Antimicrobial activities, Microscopic analysis.