title: Effects of freezing on the bactericidal activity of human milk.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Neonatology, Hacettepe University Ihsan Dogramaci Children's Hospital, Ankara, Turkey. stakci@gmail.com
authors.forename: Sahin
authors.initials: S
authors.lastname: Takci
authors.forename: Dolunay
authors.initials: D
authors.lastname: Gulmez
authors.forename: Sule
authors.initials: S
authors.lastname: Yigit
authors.forename: Ozlem
authors.initials: O
authors.lastname: Dogan
authors.forename: Kezban
authors.initials: K
authors.lastname: Dik
authors.forename: Gulsen
authors.initials: G
authors.lastname: Hascelik
mesh_terms: D000293:Adolescent; D000328:Adult; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004926:Escherichia coli / Q000187:drug effects*; D005260:Female; D061353:Food Storage; D005615:Freezing; D006801:Humans; D007223:Infant; D007225:Infant Food; D007774:Lactation; D008895:Milk, Human; D011550:Pseudomonas aeruginosa / Q000187:drug effects*; D012034:Refrigeration; D055815:Young Adult
chemical_list: D000900:Anti-Bacterial Agents