Comparison of the fluorescent redox dye 5‐cyano‐2,3‐ditolyltetrazolium chloride with p‐iodonitrotetrazolium violet to detect metabolic activity in heat‐stressed Listeria monocytogenes cells

摘要

The fluorogenic redox indicator 5‐cyano‐2,3‐ditolyltetrazolium chloride (CTC) was compared with the chromogenicp‐iodonitrotetrazolium violet (INT) and conventional methods to assess cellular viability. Mild heat treatment was used as a well‐controlled method for producing non‐viable and sub‐lethally injured cells. CTC gave an underestimation of the viability ofListeria monocytogenescells when compared with classical plating methods whereas INT gave an overestimation. However, CTC proved to be a sensitive indicator of uninjured cells. The difference between the total count and the CTC count was equivalent to the injured cell population. The fluorescent formazan formed on reduction ofCTC was readily detected with a charge coupled device and cells enumerated automatically using i