Effects of freezing and thawing and storage by freezing on the biological and morphological properties of strain K-9 of Klebsiella pneumoniae and its variants.

Using strain K-9 of Klebsiella pneumoniae and its variants A, B and C, which possess a large, small, or extra-small capsule or are unencapsulated, and exhibit high, middle, or low mouse virulence or avirulence in the mouse, respectively, the effect of freezing and thawing on the protection and storage by freezing in 20% skim milk solution on their biological and morphological properties was investigated. Experimental results showed that these organisms were sensitive against freezing and thawing in the order variant C, the parent strain, variants A and B. 20% skim milk solution was the most favourable for survival of the organisms compared to trypticase soy broth and 10% glycerol. Their mouse virulence was similarly sensitive to freezing and thawing experiments although no alteration of their biochemical properties was observed. When the organisms were suspended in 20% skim milk solution and stored for 2 years at -70 degrees C, their mouse virulence was not altered. When morphological features were tested electron microscopically, cellular injuries such as vacuola or fissions of cell walls were observed in the variants but not in the parent strain. However, it was evident that conversion to unencapsulation from encapsulation occurred at a high frequency in the parent strain and in variant A when determined by the colonial morphologies in soft-agar medium.