Bacteriological Safety of Human Milk Storage

[ABSTRACT] Human milk is the optimal food for infants because it fulfills their nutritional requirements and strengthens the bond between mother and child. However, because mothers have increasing difficulty continuing to breastfeed because of the demands of modern life, expressed milk is often stored for later use. This study examined the effects of different storage methods on bacterial counts and species in expressed human milk. Samples of human milk from 20 healthy lactating mothers were stored frozen for 4 weeks, refrigerated for 24 or 48 hours, or left at room temperature for 3 or 6 hours. The samples were then analyzed for bacterial counts and species and compared with freshly collected samples. The bacterial counts of frozen and refrigerated samples of human milk were significantly lower than those in fresh samples, whereas those of samples left at room temperature were significantly higher. However, bacterial counts were not zero, even after refrigeration or freezing, which suggests that bacterial counts depend on the number of bacteria present when the milk was collected. The bacterial species present did not change, regardless of the storage method, which suggests species composition also depends on the species present at the time of collection.