Bacterial and fungal growth after freezing or refrigerating parenteral nutrient solutions

Parenteral nutrient (PN) solutions were evaluated for growth of pathogenic organisms after refrigeration or freezing and then thawing. Sixteen bags of hypertonic dextrose and amino acid solutions were divided into two series (refrigerated and frozen), inoculated with Escherichia coli. Candida albicans, Staphylococcus aureus, or Streptococcus faecalis, and exposed to freezing or refrigeration. The inoculum concentration was greater than would likely occur with patient contamination of the solution. Microbial growth in the solutions was determined after warming to room temperature and at 17 or 18 hours after reaching room temperature. There was no increased growth of C. albicans in PN solutions that were frozen versus the refrigerated samples. Counts for all of the organisms in the frozen series, immediately after freezing and then thawing, decreased or stayed the same compared with baseline counts. Growth of E. coli, Staph. aureus, and Strep. faecalis increased in the frozen samples compared with the refrigerated samples after room-temperature storage, suggesting a possible increased risk of infectious complications if contaminated solutions are left at room temperature for extended periods. Since no increased risk of microbial growth is likely in frozen versus refrigerated PN solutions that are thawed and promptly infused, batch freezing may be an effective and convenient means of preparing PN solutions for home patients.