AN IMPROVED DIRECT VIABLE COUNT FOR THE ENUMERATION OF BACTERIA IN MILK

The direct viable count (DVC), a microscopic method for the enumeratio n of Viable bacteria, was modified by replacing nalidixic acid with ci profloxacin. This modification made it possible to apply this method t o a variety of Gram-negative and Gram-positive bacteria which was not previously possible. Of the four antibiotics tested (nalidixic acid, n ovobiocin, ciprofloxacin and mitomycin C), ciprofloxacin and mitomycin C were the only ones effective for use in the DVC with all of the bac teria tested. In addition, ciprofloxacin could be used at a single con centration (1 mu g/ml) while adjustments were necessary with the other antibiotics when examining bacteria from different genera and, in som e instances, from different species. The use of ciprofloxacin in the D VC resulted in viable cells that had elongated by 5-11 times their ori ginal length. We conclude that the modified DVC will be useful in grow th and survival studies of bacterial pathogens and spoilage organisms in milk and other foods.