Identification and quantification of lichenysin – a possible source of food poisoning

Abstract

Lichenysin produced by 53 different Bacillus licheniformis strains has been structurally examined with a qualitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) method using quadrupole-time-of-flight mass spectrometry. The same lichenysin isoforms are produced from all strains, indicating that the growth conditions have a stronger influence on the lipopeptide production than the genotype. A rapid method for the quantification of lichenysin from bacterial cell cultures with LC-MS/MS after a simple methanol extraction has been refined. For the first time commercially available lichenysin has been used as calibrant, making quantification more accurate. The trueness for C15-lichenysin has been improved to 94% using matrix-matched calibration with lichenysin compared with 30% using solvent calibration with surfactin. The quantitative method was fully validated based on Commission Decision 2002/657/EC. The LOD of the method was below 1 µg g^–1 and the repeatability ranged from 10% to 16%.

Keywords:

• lichenysin
• LC-MS/MS
• quantification
• validation
• Bacillus licheniformis

Acknowledgements

The authors thank Kristin O’Sullivan and Toril Lindbäck for their invaluable help in performing the bacterial growth experiments.