Profiling of the microbiota of breast milk before and after feeding with an artificial nipple

Breast milk is a valuable and useful source of nutrition; however, surplus milk is routinely discarded for hygiene reasons despite an unclear scientific basis. Here, we profiled the microbiota of expressed breast milk before and after feeding with an artificial nipple and examined the bacterial survival in breast milk stored at 4 °C.

Eleven mother-baby pairs were included in the study. Samples of expressed breast milk were collected before and after feeding with an artificial nipple and examined both immediately (0 h) and after storage for 3 and 12 h at 4 °C. Each sample was inoculated onto a blood agar plate and incubated anaerobically and aerobically at 37 °C. Genomic DNA was extracted from individual bacterial colonies, which were identified by 16S rRNA gene sequencing.

Before feeding, the bacterial counts at 0 and 12 h were (1.4 ± 1.6) × 10⁵ colony-forming units (CFU)/mL and (1.4 ± 0.6) × 10⁵ CFU/mL, respectively. Staphylococcus (47.7% and 41.9%, respectively), Cutibacterium (20.7% and 36.0%, respectively), and Streptococcus (16.1% and 6.6%, respectively) were identified among the samples. In contrast, after feeding, the bacterial counts at 0 and 12 h were (2.7 ± 1.7) × 10⁵ CFU/mL and (2.1 ± 2.5) × 10⁵ CFU/mL, respectively. Staphylococcus (30.1% and 37.4%, respectively), Cutibacterium (11.7% and 31.7%, respectively), and Streptococcus (41.5% and 25.2%, respectively), were identified among the samples.

Bacteria were present in the breast milk before feeding. Although the main component of the microbiota shifted from Staphylococcus to Streptococcus species after feeding, these results suggest that surplus expressed breast milk may be preserved safely in a refrigerator for at least 12 h after feeding with an artificial nipple.