P125: Utilization of membrane color to facilitate the detection of microbial colonies

Membrane filtration offers many advantages for the detection, enumeration, and presumptive identification of microorganisms. Moreover, there are many choices of microbial growth media. These choices include the use of selective versus nonselective media, and the use of media that contain dyes to stain the microbes. Some of the more popular medial formulations for the total count of microbes do not contain colorizing agents, such as R2A. Environmental sampling of potable or purified water often involves the detection of microbes living in low nutrient conditions. These oligotrophic microbes often form small slowly growing colonies that can be a challenge to detect on white membranes with black grids. However, the use of colored membranes, such as green membranes with dark green grids, can facilitate the detection and enumeration of these small undyed colonies. In this experiment, we show how the use of green membranes makes it easier to detect small undyed colonies for the routine analysis of potable and purified water.