Proposed Method for the Bacteriological Examination of Flat Surfaces

Abstract

A contact plate method has been developed for determining the type and extent of bacterial contamination remaining on flat-surfaced eating utensils, dairy equipment, etc., after cleaning. The contact plate consists of a sterile flattened tin can coyer, 37/16 inches in diam., aseptically filled with agar and kept in a sterile Petri dish. A test is made by placing the contact plate on the surface to be examined for 4 seconds, returning the contact plate to the Petri dish, and later counting the colonies which have developed during incubation at 32[degree] C. The contact plate method was found to recover more organisms from the tested surface than a wooden swab method or a flexible wire swab method but fewer organisms than a stiff wire swab method. Possible explanations for this fact are discussed. Approx. 50 field tests showed the contact plate method to be a practical, simple, and rapid means of obtaining an indication of the contamination which exists on flat-surfaced utensils and equipment.