Determination of bacterial numbers on tableware by means of direct plating.

It has long been recognized that swabbing methods will not remove all or even a fixed percentage of bacteria from surfaces. Because of this, it is not possible to use these methods for quantitative determinations with any degree of accuracy. Considerable work has been done to develop methods that will permit greater recovery of bacteria from tableware. Higgins (1950) and Cain and Steele (1953) have used swabs made of calcium alginate. After use, these swabs were placed in a diluent containing sodium hexametaphosphate. On shaking, the swabbing material dissolves, thereby eliminating the problem of removing bacteria from the swab. However, there is no information to indicate that this material is any more effective than cotton in removing bacteria from a surface. Olsen and Hammer (1933) developed an agar disc method for studying bacterial contamination on metal surfaces. While this method will recover greater numbers of bacteria than swab tests, it will not remove bacteria from cracks and inaccessible areas. The contact method of Walter and Hucker (1941), which is a modification of Olsen and Hammer's method, and the quantitative method of Guiteras et al. (1954) have relatively the same deficiencies. In an attempt to obviate the deficiencies in the above methods, an investigation was made to modify the agar disc method. The modification investigated was to grow the bacteria in situ by placing liquid agar medium on table ware, allowing it to harden and then incubating the utensil.