Objectives: Storage of human milk by freezing has been recommended for long-term storage. The present study analyzed the bactericidal activity of human milk on Escherichia coli and Pseudomonas aeruginosa and determined the changes in bactericidal activity following freezing at −20°C and −80°C for 1 month and 3 months.
Methods: Forty-eight milk samples were collected from 48 lactating mothers. Each sample was divided into 10 aliquots. Two of the samples were processed immediately and the others were stored at both −20°C and −80°C until analysis after 1 month and 3 months of freezing.
Results: All of the fresh milk samples showed bactericidal activity against E coli and P aeruginosa. Freezing at −20°C for 1 month did not cause statistically significant alteration in bactericidal activity (P > 0.017), whereas storage for 3 months lowered the degree of bactericidal activity significantly (P < 0.017) against E coli. Bactericidal activity was protected when the samples were stored at −80°C. There was no statistically significant difference in the bactericidal activity of human milk against E coli between freezing at −20°C and −80°C for 1 month (P > 0.017); however, when milk was stored for 3 months, −80°C was significantly more protective (P < 0.017). Freezing at −20°C and −80°C for 1 month and 3 months did not cause any significant change in bactericidal activity against P aeruginosa (P > 0.05).
Conclusions: Storage by freezing at −80°C is more appropriate to keep bactericidal capacity of stored human milk >1 month if affordable and available, especially in intensive care settings.
*Department of Neonatology, Hacettepe University Ihsan Dogramaci Children's Hospital
†Department of Clinical Microbiology, Hacettepe University School of Medicine, Ankara, Turkey.
Address correspondence and reprint requests to Sahin Takci, MD, Department of Neonatology, Hacettepe University Ihsan Dogramaci Children's Hospital, 06100 Ankara, Turkey (e-mail: firstname.lastname@example.org).
Received 17 November, 2011
Accepted 9 February, 2012
The authors report no conflicts of interest.