3.2 Antimicrobial effects of the bioactives in B. cusia
The contents of indole alkaloids, mainly including indican, indoxyl,
indigo and indirubin, were very different after the pretreatment of the
fresh leaves of B. cusia at different temperatures (Fig. 1). To
investigate the antibacterial activities of the different bioactives,
the consumption of carbon sources and secondary metabolites duringS. aureus culture with different inhibitors was measured. As
shown in Fig. 2, the temperature had a strong effect on the
antibacterial activity of the extract. When the bioactives extracted
under the condition of 100 ℃ were used, the consumption of glucose and
the production of acetic acid did not differ from those of the control
group, indicating that there were no inhibitors in the bioactives
extracted under the conditions of 100 ℃. As shown in Fig. 1, there was
only indican in the extract under the condition of 100 ℃ without indigo,
indirubin and indoxyl. This result indicates that indican had no
inhibitory effect on the growth and metabolism of microorganisms. When
the bioactives extracted at 70 ℃ were used, the consumption of glucose
and the generation of acetic acid were the slowest, indicating that the
bioactives extracted at 70 ℃ had the strongest inhibitory effect on the
growth and metabolism of microorganisms. As shown in Fig. 1, the
bioactives extracted at 70 ℃ contained indigo, indirubin and indoxyl and
its indoxyl content was significantly higher than other bioactives.
Therefore, it could be considered that indoxyl should have a strong
inhibitory effect on the growth and metabolism of microorganisms.