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.
The fluorogenic redox indicator 5-cyano-2,3-ditolyltetrazolium chloride (CTC) was compared with the chromogenic p-iodonitrotetrazolium violet (INT) and conventional methods to assess cellular viability. Mild heat treatment was used as well-controlled method for producing non-viable and sub-lethally injured cells. CTC gave an underestimation of the viability of Listeria monocytogenes cells 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 of CTC was readily detected with a charge coupled device and cells enumerated automatically using image analysis.
Bovill
R A
RA
Institute of Food Research, Reading, UK.
Shallcross
J A
JA
Mackey
B M
BM
D001431:Bacteriological Techniques; D015169:Colony Count, Microbial; D004396:Coloring Agents; D005069:Evaluation Studies as Topic; D005456:Fluorescent Dyes; D006358:Hot Temperature; D008089:Listeria monocytogenes / Q000254:growth & development / Q000378:metabolism*; D010078:Oxazines; D010084:Oxidation-Reduction; D013778:Tetrazolium Salts
D004396:Coloring Agents; D005456:Fluorescent Dyes; D010078:Oxazines; D013778:Tetrazolium Salts; C075453:5-cyano-2,3-ditolyltetrazolium; C013574:iodonitrotetrazolium; C005559:Meldola blue