Abstract: A filter assembly for fluid containing microbial agents comprises a base ining a first broad filter supporting surface for receiving an appropriate microbial filter membrane, and at least one fluid drain disposed therebeneath to conduct the fluid carrying the microbial samples away from the filter membrane. One or more cover plates may be detachably mounted over the filter supporting surface of the base to sandwich the filter membrane. The cover plates define a corresponding number of tapering inlet ports in axial alignment with the fluid drains disposed in the base to assist in the rapid passage of the microbe-containing fluid to the filter membrane. The inlet ports terminate in reduced-diameter orifices, and ring-like projections annularly disposed about the orifices compress the filter membrane between the cover plate and the base, and form a fluid-tight sandwiching seal that prevents the microbe-containing fluid from escaping past the exposed filter area.