A method of measuring microbial activity of microbes in real time includes preparing a medium to enable microbial activity and placing the medium in operative contact with an appropriate sensor. The sensor is scanned to provide measurement electrical signals representative of position and amount of microbial activity, the sensor being responsive to a by-product of the microbial activity, such as a change in pH. The measurement signals can then be processed to provide a visual image display, and the display can visually distinguish between levels of pH activity and coordinate positions of the microbial activity.