Abstract: This study aims to measure the antimicrobial spectrum of fermentation broth of Bacillus amyloliquefaciens AF1 and to explore the activity stability and mechanism of anti-MRSA,for providing an experimental basis in seeking new anti-MRSA compounds. The drug-resistant S. aureus SA46 was used as indicating pathogen,the rest antimicrobial activities of AF1 fermentation broth were detected after it was dealed with different pH,temperatures and proteases. The antmicrobial mechanism was studied preliminarily by observing the morphologic change of SA46 tread with AF1 fermentation broth under both optical microscope and transmission electron microscope,and by detecting the protein and DNA leakage of treated SA46 with AF1 fermentation broth with SDS-PAGE and agarose gel electrophoresis. The results showed that AF1 fermentation broth had a broad antimicrobial spectrum. It presented a strong inhibitory ability to all tested clinical drug-resistant Staphylococcus aureus,common clinical Escherichia coli and S. aureus；also it inhibited the most of the tested phytopathogen. The antimicrobial activity of AF1 fermentation broth remained more than 95% in pH 2.0 - 9.0 for 120 min from 4 to 80℃,and it was stable when adding protease K,pepsin and trypsin into the broth respectively. The cell walls of SA46 treated by AF1 fermentation broth（MIC）were destroyed at varied level while observed under both optical microscope and transmission electron microscope. Furthermore,the leakage of protein and DNA of treated SA46 with AF1 fermentation broth were checked by SDS-PAGE and agarose gel electrophoresis. The electrophoretic bands of experimental groups were clear,while there was no bands in control groups on both DNA and protein electrophorograms. Thus,a preliminary deduction was that the cell walls of MRSA were damaged by AF1 fermentation broth. In conclusion,B. amyloliquefaciens AF1 might be developed as a potential new source for the novel anti-MRSA medicines.

Key words: Bacillus amyloliquefaciens, antimicrobial spectrum, anti-MRSA, cell wall