Skim milk enhances the preservation of thawed −80 °C bacterial stocks

Abstract

The results from bacterial strain recovery efforts following hurricanes Katrina and Rita are reported. Over 90% of strains frozen in 10% skim milk were recovered whereas various recovery rates were observed for glycerol-stored stocks (56% and 94% of E. coli, depending upon the laboratory). These observations led to a viability comparison of Streptococcus pyogenes, Campylobacter jejuni, Borrelia burgdorferi, Salmonella enterica subsp. Typhimurium, Pseudomonas aeruginosa and Escherichia coli strains stored in glycerol or skim milk. In all bacteria examined, 10% skim milk resulted in significantly longer viability after thawing than 15% glycerol solutions currently used in most laboratories.

The Family Campylobacteraceae

“…Cultures may be stored for up to a week under microaerobic conditions at 4 C. For longer-term storage, cultures can be frozen in a cryopreservative, such as 10 % skim milk (Cody et al 2008) or 5 % glycerol, and stored at À80 C or in liquid nitrogen. Cultures can last for years but may require enrichment for recovery of damaged cells.…”

Growth and Laboratory Maintenance of Pseudomonas aeruginosa

“…P. aeruginosa can be preserved in frozen stocks of either 20% glycerol or 10% skim milk (Cody et al, 2008) that can be stored at −80°C. Growing bacteria on fresh plates from frozen stocks is important when starting experiments to ensure consistent results, particularly for clinical isolates from CF samples, as they can have very high mutation rates.…”

“…It has been reported that viability of frozen stocks may be improved when they are prepared in 10% skim milk instead of glycerol ( Cody et al, 2008). …”

Evaluation of three methods for preservation of Azotobacter: freeze-drying, cryopreservation, and immobilization in dry polymers

“…Under some circumstances refrigeration and freezing could be impracticable (Cody et al 2008). Hence, to maintain microbial cultures at room temperature is paramount.…”

“…Bacterial strains and culture preparation: Strains C26 and C27 were isolated from eucalyptus rhizosphere in Codazzi, Cesar, Colombia (Obando (Cody et al 2008, and routine method in our Lab) since these show to be highly effective to preserve viability of many Gramnegative bacteria. Finally, for immobilization in dried polymers we used alginate (Bashan and Gonzales 1999), acacia gum (Krumnow et al 2009), carrageenan (Denkova et al 2004), and Polyox ® that was first evaluated in this study.…”