Optical method and device for the detection and enumeration of microorganisms

An apparatus for detecting the presence of microorganisms in a test sample comprising:

• optical instrumentation including a light source unit and a photodetector;
• a container with at least one section transparent to light;
• a growth zone configured to receive the test sample, the growth zone located in the container, containing a mixture of liquid growth media capable of supporting growth of the microorganisms, at least one dye indicator dispersed in the growth media, the dye indicator composed of material that chemically interacts with metabolic products of growing microorganisms to effect color change of the dye indicator;
• a detection zone, the detection zone configured to detect the presence of growing microorganisms, the detection zone located in a container adjacent to the transparent section and containing an identical mixture of the liquid growth media and the dye indicator substrate;
• a hydrophilic membrane interposed between said growth and detection zones, the membrane configured to allow diffusion of molecules of the liquid growth media, the dye indicator, and molecules of the metabolic products of growing microorganisms, back and forth between the growth and the detection zones, wherein the membrane is configured to prevent microorganisms and particulate matter of the test sample from penetrating into the detection zone;
• and
• wherein said light source produces light that passes through said detection zone prior to being detected by said photodetector and wherein changes in the color of the dye indicator in the detection zone indicate presence of microorganisms growing in the growth zone.