Objective: To clarify the antimicrobial constituents of endophytic Gibberella intermedia from the Polygonum capitatum and investigate their reversal effect on the resistance of multi-resistant bacteria. Method: The active components of G. intermedia were isolated and purified by modern separation techniques on the basis of bioassay-guided method. Their structures were identified by spectroscopic methods including modern mass spectrometry (MS) and nuclear magnetic resonance (NMR) analysis. The antibacterial activity was tested on a 96-well plate to screen the active antimicrobial constituents

while their reversal effects on the resistance of multi-resistant bacteria were determined by evaluating their effect on the minimum inhibitory concentration (MIC) of the quinolones. Result: Six compounds were isolated from the extracted metabolites of G. intermedia

and their structures were identified as fusaric acid (1 )

indole-3-acetic acid (2 )

p-hydroxyphenylacetic acid (3 )

protocatechuic acid (4 )

o-hydroxyphenylacetic acid (6 )

and p-hydroxybenzaldehyde (6 ). Compounds 2-6 were isolated from metabolites of G. intermedia for the first time. The MICs of compound 1 against clinically resistant Escherichia coli

Staphylococcus aureus and Proteus mirabilis were 31.3

125

and 62.5 mg · L-1

respectively. Compound 1 showed the reversal effect on drug resistance. In the presence of 1/8 MIC of compound 1

the MICs of levofloxacin and ciprofloxacin against the resistant E. coli were reduced by 4 and 2 folds respectively. In the presence of 1/4 MIC of compound 1

the MICs of levofloxacin and ciprofloxacin against the resistant P. mirabilis were reduced by 2 and 4 folds respectively

and 2 folds respectively against the resistant S. aureus. Conclusion: Fusaric acid was the main antimicrobial ingredient of G. intermedia

showing reversal effects on the multidrug-resistant E. coli

P. mirabilis and S. aureus. This study laid the foundation for treatment of multi-drug resistant urinary tract infection and improving the treatment efficiency of quinolones in urinary tract infection.