Direct epifluorescence filter technique DEFT

Direct counting can be improved by the use of fluorescent dyes, such as acridine, especially if combined with the recovery of cells by membrane filtration. Direct epifluorescent filter techniques (DEFT) are used in the milk and dairy industries to estimate both bacteria and fungi. They can produce results in less than 25 minutes which correlate closely with traditional methods. Further developments have automated the counting procedure by the use of image analysers thus removing the problem of operator fatigue. 

Splittstoesser (1992) described a method using fluorescent dye (acridine orange) known as direct epifluorescence filter technique (DEFT), a method also applied by Divol and Lonvaud-Funel (2005). Divol and Lonvaud-Funel (2005) used a different substrate, fluoresceine diacetate, which is hydrolyzed by viable cells to form a fluorescent product, fluoresceine. However, Atlas and Bartha (1981) observed that cell population values can differ substantially between (epifluorescence and direct plating) methods (10 vs. 10 CFU), possibly due to the presence of viable-but-non-culturable cells. In addition, Meidell (1987) reported interference... 

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