Colony Count Accuracy Using Selective Media: Analysts Versus Automatic Colony Counters ^{1, 2}

Using two different methods of counting, a comparison was made of the ability of five analysts to enumerate colonies on selective bacteriologic media. First, analysts manually counted the colonies aided by a Quebec colony counter and a hand tally. This was followed by the counting of colonies on each of three automated colony counters. In this pilot study, the media used included violet red bile agar. KF streptococcal agar, sulfite-polymyxin-sulfadiazine agar, and Standard Methods agar with 2,3,5 triphenyltetrazolium chloride added. The analysts' ability to count colonies on selective media by the manual method was superior to results obtained with the automatic colony counters.