Initial purification of antimicrobial fermentation metabolites from Paecilomyces cicadae and its antimicrobial mechanism

In present study, the antimicrobial compounds (AMCs) from Paecilomyces cicadae (P. cicadae) were initially purified, and its antimicrobial mechanism was investigated. The results showed that the molecular weight of AMCs in crude protein extracts was below 10 kDa. The minimum inhibitory concentration (MIC) of crude protein extracts against Escherichia coli (E. coli) was 0.050 mg/mL. After E. coli was treated by crude protein extracts, we found that it could disrupt the structure of cell membrane, change the content of whole-cell or membrane proteins. In addition, crude protein extracts with certain concentrations also could effectively interact with bacterial DNA. Quantitative real-time PCR (qRT-PCR) results indicated that the expression levels of flagellar biosynthesis genes fliP, fliO, flgD and flhB were down-regulated, whereas dppF and dnaJ which are associated with the transport across the membrane and the interaction with dnaK, respectively, were up-regulated when E. coli was exposed to crude protein extracts. The present findings suggested that AMCs from P. cicadae showed a potential value for the development of antibacterial products. •The antibacterial compounds were initially isolated from fermentation of P. cicadae.•One of the bactericidal mechanism from fermentation compounds was due to the change of cell structure.•The fermentation compounds could bind with cellular DNA, and affected the expression of related genes.