Efficacy of Peptone-glycerol Broth in Long-term Storage of the Bacterial and Yeast Cultures

Introduction: Bacterial isolates and control strains stocking is an integral part of clinical microbiology laboratories. This is an essential step in maintaining quality. Preserving the strains without altering the character is an essentiality. There are different stock culture preparations studied in past showing varied level of performance. Aim: To evaluate the performance in terms of longevity and phenotypic character preservation of Peptone Glycerol Broth (PGB) in comparison to Brucella Glycerol Broth (BGB) and Skim Milk (SKM). Materials and Methods: The present study was a prospective analytical study. Three quality control strains and seven clinical isolates with different types of resistance were stocked in triplicates with cryobead based peptone broth with 15% glycerol, Brucella Broth (BB) with 15% glycerol and 10% SKM and stored at -80 degrees C. Isolates were revived in monthly pattern, quarterly pattern and once after 10 months to assess the variations in viability and loss of phenotypic properties arising out of repeated freeze thaw and contaminations. Viability was assessed by time taken to produce observable confluent growth on revival. Metabolic characters and antibiotic susceptibility testing were compared before and after stock revival at intervals. Results: The phenotypic characters like metabolic features and antibiotic susceptibility were preserved with all three preparations both with repeated freeze thaw and single freeze thaw at the end of 10 months. PGB and BGB had a 100% revival rate of stored isolates with a confluent growth at 24 hours in comparison to 93.56% with SKM. Conclusion: Cryobead preparation of peptone broth-15% glycerol can be used as an effective preparation for stock culture maintenance of non-fastidious bacteria and yeast.