bacterial viability assay

[Sylvie Chauvaux]

Hello,

Does somebody know an assay to follow bacterial viability of a 
culture ? The commercial kits implicate to take samples of cultures. 
Since I need to follow the viability overnight, I need an assay where 
the reagents can be present in the culture without affecting growth 
of bacteria.

Many thanks for all your ideas,

Sylvie