Acta Scientifica Malaysia (ASM)

Bacterial endophytes, dwelling in the internal tissues of plants, have been reported to secrete many biologically active secondary metabolites which have found useful medical applications. This study aimed at evaluating antibacterial and antioxidant activity of endophytic bacteria from Hibiscus rosa-sinensis flower. Fresh flowers were collected and identified. Endophytic bacteria were isolated by imprint method after proper sterilization. Cultural and polymerase chain reaction were used to confirm the identity of the bacterial endophyte. Four clinical bacterial isolates including Salmonella enterica, Klebsiella pneumoniae, Escherichia coli and Staphylococcus aureus, were collected from Cottage hospital and identified culturally. Isolated endophytic bacteria were screened for antimicrobial potential using agar well diffusion method. Crude metabolite was prepared by centrifugation of broth culture of the bacterial isolates. Antibacterial activity of the crude metabolites was carried out by agar well diffusion while its antioxidant activity was done using DPPH and FRAP assays. Different compounds and their functional group present in the crude metabolites were detected using GC-MS/FTIR analyses. Antibiotic resistance of the clinical isolates was carried out by disk diffusion. Isolated bacterial endophytes included Bacillus cereus, Bacillus thuringiensis, Bacillus subtilis, Bacillus amyloliquefaciens and Bacillus siamensis. Screening test revealed Bacillus cereus to have the highest antibacterial potential of 50%. At 100% concentration of Bacillus cereus metabolite, zones of inhibition ranged from 6.67±0.80mm in Staphylococcus aureus to 17.33±1.20mm in Salmonella enterica. Minimum inhibitory concentration of the metabolite ranged from 25% in Salmonella enterica to 100% in Klebsiella pneumoniae while minimum bactericidal concentration was only observed against Salmonella enterica at 100%. The four clinical isolates were multidrug resistance with resistance index ranging from 0.5 to 1. Percentage reduction of DPPH increased from 9.2% at 10% concentration of crude metabolite to 53% at 100% concentration, although lower than that of the ascorbic acid. However, the crude metabolites reduced FRAP better than ascorbic acid. Compounds present in the crude metabolite of Bacillus cereus included butylated hydroxytoluene, undec-10-ynoic acid, squalene and oleic acid. This study has shown that endophytic Bacillus cereus from Hibiscus rosa-sinensis flower is a rich source of biologically active metabolites.