Comparative evaluation of three in vacuo dessication procedures on bacterial cultures

The paper presents results obtained for the bacterial cultures preservation (E. coli ATCC 25 922 and S. aureus Wood) by three in vacuo desiccation procedures: freeze-drying (lyophilization or cryo-desiccation at eutectic zone), cryo-desiccation above eutectic zone and direct drying. It has been in view: the survival of liquid cultures as reported to the desiccation procedure per se, the loss of viability of desiccated cultures stored in refrigerator for at least one year and the residual moisture of desiccated cultures. For 3 batches there has been applied the accelerated thermal degradation test. Employing the same protective medium for both cultures, E. coli cultures prove to be more easily affected by lyophilization and cryo-desiccation above eutectic zone as compared to S. aureus cultures, fact that may be due to the differences between the wall structures of G--bacteria and G+ bacteria, respectively. During storage, E. coli and S. aureus cultures proved a quite similar loss of viability. The residual moisture content was quite similar for both E. coli and S. aureus cultures exposed to the same in vacuo desiccation procedure. The lyophilization and the cryo-desiccation above eutectic zone, as compared to direct drying, yielded superior results. The accelerated thermal degradation test provides only informative results, partially confirmed by viable counts determined at stated intervals of storage time in the refrigerator.