Comparison of preservation media and freezing conditions for storage of specimens of faeces

Abstract

To evaluate the long-term recoverability of bacterial enteropathogens, two freezing conditions (deep-freezing at -70 degrees C and liquid nitrogen) and three preservation media (Cary-Blair, Amies, and buffered glycerol-saline) were tested. These were compared with storage in containers with no preservation medium and refrigeration at 4 degrees C. At 4 degrees C, viability of organisms could not be consistently maintained beyond one month; Cary-Blair medium generally gave the best results and storage without preservation medium was the least efficient. Storage in liquid nitrogen and deep-freezing effectively preserved all organisms except Campylobacter jejuni for the entire period of study (12 months). There was no difference between the various preservation media, or between storage with or without medium. Storage in preservation medium was superior to storage without such supplement for C. jejuni. We conclude that most enteropathogens survive in faecal specimens for as long as 12 months when stored at very low temperatures (-70 degrees C) whether or not preservation media are used.