This HiDip slide is recommended for total bacterial count and inactivation of disinfectants. PCA w/TTC & Neutralizers : Recommended for determination of plate counts of microorganisms in food, water, waste water & clinical . Also called as Standard Methods Agar. It is recommended by APHA and FDA for determination of counts. TTC reduction renders red colour to the colonies. Lecithin , sodium thiosulphate, tween 80 and histidine are the neutralizers.