Cold storage of human milk: effect on its bacterial composition.

OBJECTIVES

In the last few years, it has been proved that human milk contains bacteria that constitute an important factor in the initiation and development of the neonatal gut microbiota. In this context, the objective of this study was to evaluate the effect of cold storage on the natural bacterial composition of breast milk.

MATERIALS AND METHODS

Breast milk samples provided by 34 healthy women and collected either by manual expression (n = 27) or breast pump (n = 7), were plated onto several culture media immediately after arrival at the laboratory (day 0) and after storage at -20 degrees C for 6 weeks. A high number of isolates from 8 of the women were identified at the species level.

RESULTS

No statistically significant differences were observed between the counts obtained at both sampling times in those media in which growth was detected. In all of the culture media, bacterial counts in pump-collected samples were higher than in those obtained by manual expression. Staphylococci and streptococci were the predominant bacteria in both fresh and frozen samples, Staphylococcus epidermidis being the most abundant species at both sampling times. Lactic acid bacteria and bifidobacteria were also present in fresh and frozen breast milk samples, but among them, only 1 species (Lactobacillus gasseri) could be isolated at both sampling times.

CONCLUSIONS

The results of this study suggest that cold storage of milk at -20 degrees C for 6 weeks does not significantly affect either the quantitative or the qualitative bacterial composition of breast milk.