ABSTRACT
Streptococcus mutans and Streptococcus agalactiae have been reported in human oral diseases including cariesand periodontitis. Thus, the present study was performed to investigate the effect of ethyl acetate crude extract ofLasiodiplodia pseudotheobromae IBRL OS-64, an endophytic fungus isolated from Ocimum sanctum leaf againstS. mutans and S. agalactiae. Disk diffusion and broth microdilution assays were used to determine the antimicrobialactivities with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values.Meanwhile, the microscopic analysis was used to study the structural degeneration of bacterial cells. The fungal crudeextracts demonstrated favorable antibacterial activity toward both test bacteria and produced an inhibition zone rangingfrom 16.0 to 21.2 mm. The MIC and MBC values of the fungal crude extract toward S. mutans and S. agalactiae weredetermined and the results showed that the MIC and MBC values were in the range of 125–500 µg/ml and 125–1,000µg/ml, respectively. The time-kill study suggested that the ethyl acetate crude extract possessed bactericidal effectwith concentration and time-dependent. Structural degeneration studies revealed the major abnormalities occurredto S. mutans cells after treated with the fungal crude extract where completed alterations of their morphology withthe formation of cavities and collapsed cells beyond repair occurred. Therefore, the current study suggested the ethylacetate crude extract of L. pseudotheobromae IBRL OS-64 could be an effective antibacterial agent to treat oral cavitybacteria.