Studies on the Preparation, Standardization and Preservation of Lepromin

VII. Changes in the Bacterial Count and the Potency of Lepromin during Preservation

Abstract

For the standardization of lepromin, it is necessary to know the available period of potency, and also to run a trial on prolonged preservation by the freeze-dry procedure. A batch of lepromin was divided in two parts; one part was lyophilized without addition of phenol and preserved in a refrigerator for 3 and 5 years, while the other part was kept, as a suspension containing phenol, in a refrigerator for the same period. After the storage, the lyophilized lepromins returned immediately to stable suspensions with the addition of 0.5% phenol solution. The bacterial counts of these lepromins, using the pinhead method described by Hanks et al., were not different from the standard value, i.e. 150-160 million per ml, while that of the lepromins kept in a refrigerator were reduced to about 74% and 70% of the original count after 3 and 5 years, respectively.
Comparative tests with these lepromins were carried out by examining the size of the Fernandez and Mitsuda reactions in leprosy patients, the results being shown in Tables 2 and 3. It was found that the Mitsuda reactions caused by lepromin preserved as a suspension for 5 years were clearly weaker than that of the lepromin lyophilized during the same period, and that the Fernandez reactions were not different for the two lepromins. In the case of the lepromins preserved for 3 years, there was no significant difference in the potency causing the Fernandez as well as the Mitsuda reactions, whether the lepromin had been lyophilized or not.
Accordingly, it is concluded that a lepromin can be preserved for 3 years in a refrigerator without appreciable loss of potency. Lyophilization of lepromin was found to be suited for prolonged preservation, at least for 5 years, without change in the bacterial count and potency of the lepromin.