Freeze-drying of Flavobacterium columnare, Flavobacterium psychrophilum and Flexibacter maritimus

Freeze-drying of bacteria requires the use of a cryoprotective agent. Skim milk, polyvinylpyrrolidone, dextran, sodium glutamate, sucrose, horse or calf serum are all routinely used. The effects of 7 suspending media, each containing 1 of these cryoprotective additives, were studied on 3 strains each of 3 fish pathogenic gliding bacteria (Flavobacterium columnare, Flavobacterium psychrophilum and Flexibacter maritimus). The viability of preserved bacteria was evaluated by colony enumeration on Anacker and Ordal medium (Fa. columnare and Fa. psychrophilum) and on Difco marine medium 2216E (Fx. maritimus), 48 and 72 h after inoculation. The data show the 3 bacterial species to be optimally preserved in suspending media containing Difco Bacto Brucella Broth (2/3) supplemented with either horse or foetal calf serum (1/3).