Research Concerning Use of Long-Term Preservation Techniques for Microorganisms

From the large number of methods used for storage of microorganisms, the more effective methods are long-term cryopreservation and lyophilization. The temperature change rate, controls transport of water around cell membranes and indirectly likelihood of intracellular freezing. If the cooling is too fast, the membranes cannot carry water out of the cell and freezing inside. Each cell has an optimum cooling rate, while the survival of very low absolute except that cryoprotector is present to reduce freezing damage.In the present study we proposed to determine the efficiency of some techniques on long term microorganisms conservation as cryopreservation and freeze-drying and the influence of cryoprotectants used in various concentrations on survival rate of bacterial strains during cryopreservtion at -80 ° C in freezer and - 196 ° C in liquid nitrogen. These 7 bacterial strains used for this work came from our collection of cultures, and are represented by Escherichia coli, Klebsiella pneumonie, Staphylococcus aureus, Bacillus cereus, Salmonella enterica., Pseudomonas aeruginosa, Lactobacillus casei. The cryoprotectant used are: dimethyl sulphoxide (DMSO) at a concentration of 5% and 10%, ethylene glycol (EG) at a concentration of 5% and 10%, glycerol (Gl) at a concentration of 5% and 10%, propylene glycol (PG) at a concentration of 5% to 10%.