Abstract:

The easy-to-operate magnetic bead cryopreservation method has become the mainstream approach for strain storage in detection laboratories. To clarify the stability of magnetic bead cryopreservation for maintaining standard foodborne strains， this study selected 12 common standard foodborne strains， including gram-positive， gram-negative， spore-forming， obligate anaerobic， and aerobic bacteria. The plate counting method was used to determine the effects of repeated freeze-thaw cycles and different storage durations on strain viability； the VITEK2 Compact automated microbial identification system and 16S rDNA sequence analysis were employed to verify biochemical and genetic stability.The results showed that after 10 repeated freeze-thaw cycles， 9 strains （including Staphylococcus aureus and Escherichia coli，etc.） exhibited minimal fluctuations in viable counts and strong stability. In contrast， the viable count of Pseudomonas aeruginosa continued to decline， while Clostridium perfringens and Vibrio parahaemolyticus were completely inactivated after 6 freeze-thaw cycles. Under unopened storage at -70°C for 15 years， 10 strains （including S. aureus， E. coli， Bacillus cereus， etc.） maintained high viability， whereas C. perfringens and V. parahaemolyticus were almost completely inactivated. Both the VITEK 2 Compact identification and 16S rDNA sequence analysis confirmed that all strains remained stable in biochemical characteristics and genetic genotype without obvious variation after treatment. In conclusion， the magnetic bead cryopreservation method is generally suitable for the long-term preservation of common foodborne pathogenic bacteria. However， C. perfringens and V. parahaemolyticus showed poor tolerance to repeated freeze-thaw cycles， indicating the need for optimized preservation conditions. This study provides scientific data references for applications such as standardized management of strains and interim verification of strains， filling the gap in strain stability research in the domestic strain preservation field.

Key words: food-borne standard strains, porcelain beads cryopreservation method, repeated freezing and thawing, long-term preservation, stability