Optimization of fluorescence microscopy techniques for the detection of total and viable lactic acid bacteria in whey starter cultures

This work aimed at studying the applicability of the most widely used fluorescence microscopy techniques to evaluate total and viable bacteria in a complex matrix such as natural whey from Grana Padano cheese production. Fluorescein diacetate, BacLight, CTC (5-cyano-2,3-ditolyl tetrazolium chloride), DAPI (4’,6-diamidino-2- phenylindole), and acridine orange stainings were evaluated on pure cultures and optimised for their use directly on natural whey starter cultures. Different incubation times and resuspension buffers were tested. The developed procedures allow the enumeration of both viable and dead bacterial cells directly on the whey matrix. The methods proposed may be used to directly evaluate the metabolic state of bacterial populations present in whey starter cultures.