A Study of the Stuart Method for the Evaluation of Germicides

John H. Litchfield, Z. John Ordal
1955 Applied microbiology  
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
more » ... 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. MATERIALS AND METHODS Germicides Three quaternary ammonium germicides and three germicides representative of phenolic, cresylic, and pine oil types were tested. The quaternaries were Roccal,' an alkyl dimethyl benzyl ammonium chloride and two detergent sanitizers, designated "A" and "B".2 The detergent sanitizers contained 1.5 per cent alkyl dimethyl benzyl ammonium chloride as the active ingredient, a non-ionic detergent, and different proportions of inorganic buffer salts to provide different degrees of alkalinity. A 1.33 per cent solution (200 ppm of the active ingredient) of detergent sanitizers A and B gave pH values of 10.3 and 11.4, respectively. The phenol was reagent grade, mp 39-41 C. The cresylic germicide, Lysol,' contained cresylic acid, o-phenylphenol, and soap as active ingredients. The pine oil disinfectant4 contained pine oil, soap, and isopropanol as active ingredients. The test concentrations of the quaternaries were selected in the range of those recommended by the manufacturer. The phenol test concentrations corresponded to the phenol resistance values specified for each test organisms prescribed in the official phenol coefficient method of the Association of Official Agricultural Chemists (1950) and in the Stuart method. The test concentrations of the cresylic and pine oil disinfectants were determined by multiplying the Salmonella typhosa phenol coefficient at 20 C claimed on the label by 20. These dilutions were expressed in terms of parts per million. Test Organisms and Media The test organisms used were Salmonella choleraesuis ATCC 10708, specified by Stuart et al. (1953); Salmonella typhosa Hopkins 26, specified in the official phenol coefficient method; and Micrococcus pyogenes var. aureus FDA 209, specified in both methods. The cultures were maintained as prescribed in the official phenol coefficient method. Fresh broth cultures of S. choleraesuis and S. typhosa were made from the stock cultures after 28 consecutive daily transfers in FDA broth. A fresh broth culture of M. pyogenes var. aureus was made from the stock culture after 21 consecutive daily transfers in FDA broth. Letheen broth was used for the subculture medium
doi:10.1128/aem.3.2.67-71.1955 fatcat:duw6vssiubaavibgwmfx4kjphq