Opportunistic microbiota of breast milk and antimicrobial activity of milk whey at different periods of lactation

Object of study. The evaluation of the interaction between breast milk opportunistic microorganisms abundance and the milk whey antimicrobial activity at different periods of lactation.
Materials and methods. 100 samples of breast milk from healthy breastfeeding mothers were inoculated on solid selective media, and then pure cultures of microorganisms were identified by MALDI-TOF mass spectrometry. The antimicrobial activity of the whey against a model culture of Candida albicans was evaluated by spectrophotometry.
Results. 270 isolates represented by 36 species of 13 genera of opportunistic bacteria were obtained. None of the 100 samples contained opportunistic fungi. Staphylococci (7 species) and streptococci (11 species) were predominant. The most common were staphylococci — S. epidermidis (70.2%) and S. aureus (20.8%), and streptococci — S. mitis (27.7%) and S. oralis (21.8%). The total contamination (median) of opportunistic bacteria in the colostrum was 7–9 × 103 CFU/ml, transitional milk — 4 × 103 CFU/ml, mature milk — 5 × 102 CFU/ml. The antimicrobial activity of colostrum whey was 87.4–89.4%; transitional milk — 88.2%; mature milk — 63.4–81.9%. The total contamination had a high inverse correlation with the lactation period (r = –0.806) and a high positive correlation with the antimicrobial activity of whey (r = 0.699). Meanwhile, a significant decrease in contamination was noted after 1 month from the beginning of lactation, while a significant decrease in antimicrobial activity was observed after 8 months.
Conclusions. The decrease of the breast milk contamination by opportunistic bacteria during the lactation period was found to be primary compared to the decrease of the whey antimicrobial activity. Thus, changes in the whey antimicrobial protection factors occur in response to changes of the opportunistic microbiota abundance.