Fluorescent labeling of nisin Z and assessment of anti-listerial action

Biomolecule labeling by fluorescent markers has emerged as an innovative methodology for bio-analytical purposes in food microbiology, medicine and pharmaceutics due to the great advantages of this method such as precision, wide detection limits, and in vivo recognition. Fluorescent nisin Z was synthesized by linking the carboxyl group and amino group of nisin Z and 5-aminoacetamido fluorescein (AAA-flu). This new structure was fully characterized by mass spectrometry with a molecular weight of 3717.3 Da. Intracellular K⁺ leakage and transmembrane electrical potential (Δψ) were used to evaluate the antibacterial action of the labeled molecule against three listerial strains and demonstrated that nisin Z endured the labeling process without any activity loss. In vivo activity of labeled nisin was observed by confocal laser microscope which revealed its localization at the septum of listerial cell division site where the membrane-bound cell wall precursor lipid II is maximal. Fluorescent nisin Z showed its great potential as a tool to study antibacterial mechanism of action of nisin in biological systems.