Microbiological aspects of heat sterilization of medicines. II. A method for the determination of the effectiveness of a sterilization process using the bioburden and the bioburdens heat resistance.

In order to verify whether the sterilization process of 60 min at 100 degrees C for invert sugar 20% is sufficiently effective to attain the generally accepted probability of survival of maximum 1 X 10(-6), we determined the bioburden and the bioburdens heat resistance for this product. We examined 98 bottles by the membrane filtration method and found 84 bottles with 0 colony forming units (CFU's) and 14 bottles with 1-9 CFU's. Because none of the isolated CFU's was heat resistant (Bacillus species), we isolated heat resistant CFU's from the environment and determined the heat resistance in invert sugar, water and NaCl solution 0.9% of four different Bacillus species. The results in invert sugar for the most heat resistant Bacillus species were a D-value of 0.92 min at 100 degrees C. For the determination of the D-value the end-point method is the most practical one, and the D-value calculation with the most probable number method is sufficiently accurate. Because of unavoidable inaccuracies in the experimentally determined D-value, safety margins of 100% have to be taken into account in the sterilization process calculations in which these D-values are used. Hence, in our case, we have to use a D-value of 2 X 0.92 min in the sterilization process calculation for invert sugar 20%. The maximum bioburden in the examined 98 test bottles was 9 CFU's. The maximum heat resistant bioburden which must be used in sterilization process calculations may be safely fixed at 10% of the total bioburden, therefore we have to use 0.9 micro-organisms in our calculation.(ABSTRACT TRUNCATED AT 250 WORDS)