Antimicrobial activities of crude extract of xyris indica and chrysazin on staphylococcus aureus and staphylococcus epidermidis in in vitro and vivo Thai silkworm model

Abstract

S. aureus and S. epidermidis are the common causes of both community and hospital-acquired infections. One of the key factors enable pathogens to survive, colonise and proliferate in body is the ability to form biofilm. The purpose of this study was to evaluate the antimicrobial activities, inhibitory effect of biofilm formation including time of killing S. aureus and S. epidermidis of X. indica and chrysazin, the major bioactive compound found in this plant. Antimicrobial activities were determined by broth microdilution method. MIC of the ethanol extract for S. aureus and S. epidermidis were 0.5 and 1 mg/ml, whereas MIC of chrysazin for S. aureus and S. epidermidis were 1 and 2 mg/ml. Time kill studies showed that the ethanol extract exerted bactericidal activity against S. aureus and S. epidermidis at 8 and 10 h. Furthermore, the ethanol extract and chrysazin also inhibited biofilm formation of S. aureus and S. epidermidis. The extract and chrysazin showed inhibitory effect on biofilm formation in a concentration dependent manner. At concentration equal and greater than MIC of the ethanol extract and chrysazin showed inhibitory effect on biofilm formation of bacterial pathogen with statistical significance (p < 0.01). In vivo study, silkworms were utilized for efficacy testing of compounds. ED₅₀ of the ethanol extract and chrysazin were 3.08 and >5.00 mg/ml for S. aureus, whereas ED₅₀ of the ethanol extract and chrysazin for S. epidermidis were 5.33 and >5.00 mg/ml. Therefore, these findings showed that the ethanol extract and chrysazin had antimicrobial activities on S. aureus and S. epidermidis both in in vitro and in vivo. Moreover, inhibition of biofilm formation may play an important role for the mechanism of action for antimicrobial activity shown.