title: Virulence and viability of Yersinia pestis 25 years after lyophilization.
abstract: When equal volumes of 6% lactose and a broth culture of Yersinia pestis were mixed before freezing, approximately 50% of the cells survived lyophilization and reconstitution on the following day. Concomitantly, the number of viable cells per 50% lethal dose increased from about 16 to 125 organisms. On subsequent storage of the lyophilized cells under vacuum in glass ampoules at 4 degrees C for 25 years, more than 25% of the cells remained viable. When stored cultures were assayed immediately after reconstitution, virulence for mice was significantly reduced (as many as 4,000 cells/50% lethal dose), but the virulence was fully restored when reconstituted cultures were held for 24 h at room temperature, or when a subculture was prepared in fresh medium.
mesh_terms: D000818:Animals; D003470:Culture Media; D005612:Freeze Drying; D007785:Lactose; D051379:Mice; D013997:Time Factors; D014774:Virulence; D015010:Yersinia pestis / Q000472:pathogenicity* / Q000502:physiology
chemical_list: D003470:Culture Media; D007785:Lactose