Comparative evalution of capacity, carrier and suspension methods for testing the bactericidal activity of surface disinfectants

SUMMARY Comparative evalution of capacity, carrier and suspension methods for testing the bactericidal activity of surface disinfectants Key Words: Disinfectants, bacteria, test methods A series of investigations have shown that capacity, carrier and suspension methods for testing disinfectant activity give discrepant results. In this study, the bactericidal activity of 3 different disinfectants containing sodium dichloroisocyanurate, aldehydes and didecyl dimethyl ammonium chloride was evaluated using Modified Kelsey-Sykes, DGHM germ carrier and EST methods. The reasons for discrepant results were sought by keeping the bacteria, organic material and neutralization solution parameters constant in all experiments. As being a qualitative test, the results of Modified Kelsey-Sykes method were not compared with those of other two and therefore, evaluated seperately. Due to- inadequate performance control inherited in the method and being labor- intensive and time consuming, Modified Kelsey-Sykes method was found unsuitable for routine purposes. Mann-Whitney U test was used for the statistical analysis of the results obtained with DGHM and EST methods, both of which are quantitative assays. It was observed that the relationship between the results of these two methods could vary depending on the disinfectant and bacteria used in the tests. It was also observed that keeping the bacterial stocks at cold temperatures might cause changes in the susceptibilities of microorganisms to disinfectants which in turn, may affect the reproducibility of the test results. EST was found to be the most suitable method among the ones evaluated, for practical use in the laboratory.