Articles
| Open Access |
https://doi.org/10.55640/
OPTIMIZATION OF FREEZING CONDITIONS FOR CLINICAL MICROORGANISM STRAINS DURING LONG-TERM STORAGE AT -20°C
N.R. Rakhimova,Z.A. Nuruzova,A.M.Bektimirov , Tashkent State Medical University, Tashkent, Republic of Uzbekistan; Republican Specialized Scientific and Practical Medical Center for Epidemiology, Microbiology, Infectious and Parasitic Diseases of the Ministry of Health of the Republic of Uzbekistan, Tashkent, Republic of Uzbekistan Assistant of the Department of Microbiology, Virology and Immunology, Tashkent State Medical University,Doc.Sci. (Med.), Professor, Head of the Department of Microbiology, Virology and Immunology, Tashkent State Medical University.,Cand. Sci. (Med.), Senior Researcher, The Republican Specialized Scientific and Practical Medical Center for Epidemiology, Microbiology, Infectious Diseases and Parasitic Diseases.Abstract
Storage of collection microbial strains at -20°C in the absence of low-temperature equipment is accompanied by cell damage and reduced viability. Objective. To compare the effectiveness of different freezing regimes (including available two-step methods) for preserving clinical strains of 8 microbial species during long-term storage. Materials and Methods. 24 strains (E. coli, S. aureus, S. epidermidis, B. subtilis, B. cereus, K. pneumoniae, P. aeruginosa, C. albicans; 3 strains each) were stored in 20% glycerol at -20°C for 10 months. Four regimes were compared: standard (ST), programmed two-step (PZ-1: +4°C 30 min → -20°C 60 min), rapid transition through -80°C (PZ-2: 60 min in dry ice), shock freezing (ShZ: 24 h at -80°C). CFU/mL was assessed monthly. Results. PZ-2 and ShZ provided the greatest protective effect for Gram-negative bacteria: after 6 months for E. coli – 5.5±0.4 and 5.6±0.4 lg CFU/mL vs. 4.8±0.6 lg with ST (p<0.01); for K. pneumoniae – 5.2-5.3 lg vs. 4.5±0.7 lg (p<0.01). For spore-forming bacteria and C. albicans, the regime had no effect (p>0.05). Conclusions. Two-step freezing with preliminary cooling to -80°C is recommended, increasing the viability of sensitive strains by 0.5-0.8 lg CFU/mL.
Keywords
cryopreservation, freezing regimes, -20°C, clinical strains, viability, Gram-negative bacteria.
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