A QUANTITATIVE METHOD FOR ASSESSING THE EFFECT OF DISINFECTANTS AND CLEANING AGENTS ON BACTERIA DEPOSITED ON SURFACES

摘要

SUMMARY:A test has been developed for evaluating disinfectant action on surfaces, which relies on the pH response ofStrep. faecalis, since with this organism the pH of a buffered broth at the end of incubation depends on the weight of the inoculum, i.e. the numbers of organisms which survive.The organisms are deposited as a wet film on the surface of small strips of tinned mild steel, which are dried and treated with the disinfectant. The strips are finally placed in tubes of media and, after incubation, the pH is measured.The standardization of the different variables of the test are described. The condition of the test organism is particularly important: at the time the films are dried it must be in its stationary phase of growth, when the cells are homogeneous and more resistant to disinfectant action than during the logarithmic phase.Incubation is terminated when the control tubes containing strips which had no disinfectant treatment have pH values averaging 5.50. Under these conditions, with hypochlorite a linear response over the range of 0–6 p/m available chlorine is generally obtained. Chlorine may therefore be used as a standard for comparison with other disinfectants.As an example, the testing of a quaternary ammonium compound is describe