[Characteristics of a new bioindicator and its testing in practice assays of thermal disinfection methods]

Thermolysin (EC 3.4.24.4) is a thermostable metalloproteinase isolated from Bacillus thermoproteolyticus. It has been tested for its suitability as a macromolecular bioindicator for the screening of thermal disinfection methods. Using the time- und temperature-dependent inactivation rate of the immobilized enzyme we get a measure if given parameters of disinfection have been maintained. In order to determine standard conditions of practical use, physico-chemical properties of the enzyme (pH- and temperature-optimum, Km, Vmax) were ascertained first. Then, thermal inactivation of thermolysin was analyzed for temperatures between 75 degrees and 93 degrees C and exposition time 3-20 min. This new method of testing thermal disinfection is compared with conventional physical and microbiological testing methods; in addition values of reference for selected disinfection programs were analyzed. The bioindicator proved to be stable for up to 12 weeks of storage (room temperature).