A study of the Stuart method for the evaluation of germicides.

The evaluation of germicides has been the subject of considerable controversy. At the present time, the phenol coefficient method is the official procedure of the Association of Official Agricultural Chemists (1950) for the evaluation of water-soluble germicides. However, Klarmann and Wright (1946), McCulloch (1947), DuBois (1947), McCulloch, Hauge, and Migaki (1948), and Stuart, Boguskey and Fried] (1950) have questioned the accuracy of the results that are obtained when the phenol coefficient method is used for the testing of germicides differing in chemical and physical properties from those of phenolic compounds, such as the quaternary ammonium compounds. Other investigators (Stuart, 1947; Mallman and Leavitt, 1948) have criticized the phenol coefficient method on the basis that the conditions under which this method is carried out do not parallel those of actual use of the germicides, especially where it is desired to disinfect contaminated surfaces. Because of this difficulty with the phenol coefficient method, there has been considerable interest in the so-called "use dilution" methods for the evaluation of germicides. In the studies described in this paper, the use dilution method of tuart, Ortenzio, and Friedl (1953), designated as the Stuart Method, was selected as the procedure to be compared with the official phenol coefficient method as it has been accepted as a "first action" method by the Association of Official Agricultural Chemists. In this procedure, the use concentration is determined by that concentration which will disinfect the surfaces of 10 stainless steel penicillin assay cylinders in 10 minutes. The steel cylinders are contaminated by dipping in a broth culture of the test organism and dried before use. The specific objective of this study was to compare the Stuart method with the official phenol coefficient method by using various types of germicides and test organisms. In addition, studies were also made of factors that might affect the reproducibility of the Stuart method.