Isolation and characterization of a Bacillus atrophaeus strain and its potential use in food preservation

- A new Bacillus atrophaeus strain was isolated and identified.
- The strain was found to produce multiple antimicrobial agents.
- The structures of antimicrobials were confirmed by mass spectrometry and PCR.
- The antimicrobials resulted in 2-log reduction of Listeria in a model food.

Microorganisms are widely distributed in food and contribute to food safety due to production of antagonistic substances. A new bacterial strain, OSY-7LA, was isolated from a Chinese delicacy food and exhibited strong antagonistic activity against Listeria innocua. It was identified as Bacillus atrophaeus by morphological, physiological, and biochemical properties and genetic relatedness. The culture supernatant has antimicrobial activities against the Gram-positive pathogens tested, namely, Listeria monocytogenes, Bacillus cereus and methicillin-resistant Staphylococcus aureus. The antimicrobial agents were harvested by solvent extraction and were purified by high performance liquid chromatography (HPLC). Matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) and tandem mass spectrometry (MS/MS) were performed to identify these compounds. A protonated ion at m/z 3401.414 corresponded to the molecular mass of subtilosin, and the identity of the antimicrobial agent was confirmed by amplification of subtilosin gene (sbo) from isolate's genomic DNA. Sodiated ions at m/z 1030.553, 1044.642 and 1058.701 were identified as C13, C14 and C15 surfactins. LC/MS analysis proved the production of plipastatin by OSY-7LA. Supplement of crude extract of OSY-7LA supernatant in Vienna sausage that was inoculated with L. innocua showed 2-log reduction after 12 and 24 h. The new strain and related antimicrobials are potentially useful in food preservation.