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A COMPARISON OF CTC, AO, AND LIVE/DEAD CELL COUNTS IN MICROBIAL COMMUNITIES USING EPIFLUORESCENCE MICROSCOPY.  Mercedes Vieira¹, Jennifer L. Adams², Mary P. Hummerick².  ¹Fort Valley State University, Fort Valley, GA, and ²Dynamac Corporation, Kennedy Space Center, FL

     The goal of this work is to compare enumeration methods for counting bacteria in an Advanced Life Support system.  In this research, three different techniques for enumeration of bacteria in a continuous culture with wheat leachate as the feed are studied. Quantitative differences of these methods were resolved by 2 treatments, a starved system and a fed (control) system. These enumeration methods are used in the field of microbial ecology, and include CTC (5-cyano-2,3-ditolyl tetrazolium chloride) , AODC (Acridine Orange Direct Count), and Live/Dead.  The Live/Dead counts were consistent with the AO counts and impacted by the starved treatment.  CTC counts were noticeably lower in the starved treatment.