In previous years, it has been shown that human milk is a potential source of bacteria for the infant gut. The results of this work confirm the presence of the same specific bacterial strains of Bifidobacterium, Lactobacillus, and Staphylococcus in breast milk and infant fecal samples. The identity of bacteria isolated from breast milk and infant feces from 20 mother-infant pairs was investigated at the strain level. DNA from Staphylococcus, Lactobacillus, and Bifidobacterium was detected by qRTi-PCR in nearly all samples analyzed. These samples were cultured on different agar media. One colony representative of each morphology was selected and identified at the species level combining classical tests and molecular techniques (PCR, RAPD, PFGE, and/or MLST genotyping). Breast milk and infant feces from 19 mother-infant pairs shared different Staphylococcus, Lactobacillus, and/or Bifidobacterium species and strains. Significantly, 2 mother-infant pairs shared 4 bacterial strains although most pairs shared 2. These results confirm that breast milk and infant feces from mother-infant pairs share the same strain(s), indicating that breastfeeding could contribute to the bacterial transfer from the mother to the infant and, therefore, to the infant gut colonization.

Aims: Breast milk has been described as a source of bacteria influencing the development of the infant gut microbiota. Up to the present, few studies have been focused on the application of culture‐independent techniques to study bacterial diversity in breast milk. In this context, the aim of this study was to characterize the breast milk microbiota of healthy women by applying the quantitative real‐time PCR technique (qRTi‐PCR). Methods and Results: A total of 50 breast milk samples were analysed by qPCR to assess the presence of different bacterial genera or clusters, including the Bifidobacterium, Lactobacillus, Staphylococcus, Bacteroides, Enterococcus, Streptococcus, Clostridium cluster IV and Clostridium cluster XIVa–XIVb groups. Staphylococcus, Streptococcus, Bifidobacterium and Lactobacillus were the predominant groups and were detected in all the samples. Clostridium XIVa–XIVb and Enterococcus were detected in most of the samples in contrast to the Bacteroides and Clostridium cluster IV groups. Conclusions: Our results confirm the abundance of bacterial DNA in breast milk samples and suggest that the qRTi‐PCR technique has a huge potential in the microbiological analysis of human milk. Significance and Impact of the study: qRTi‐PCR allowed the detection of bacterial DNA of streptococci, staphylococci, lactic acid bacteria and bifidobacteria in the samples of human milk, which confirms that breast milk can be an important source of bacteria and bacterial DNA to the infant gut.

In this study, 20 women with staphylococcal mastitis were randomly divided in two groups. Those in the probiotic group daily ingested 10 log ₁₀ CFU of Lactobacillus salivarius CECT5713 and the same quantity of Lactobacillus gasseri CECT5714 for 4 weeks, while those in the control one only ingested the excipient. Both lactobacillus strains were originally isolated from breast milk. On day 0, the mean staphylococcal counts in the probiotic and control groups were similar (4.74 and 4.81 log ₁₀ CFU/ml, respectively), but lactobacilli could not be detected. On day 30, the mean staphylococcal count in the probiotic group (2.96 log ₁₀ CFU/ml) was lower than that of the control group (4.79 log ₁₀ CFU/ml). L. salivarius CECT5713 and L. gasseri CECT5714 were isolated from the milk samples of 6 of the 10 women of the probiotic group. At day 14, no clinical signs of mastitis were observed in the women assigned to the probiotic group, but mastitis persisted throughout the study period in the control group women. In conclusion, L. salivarius CECT5713 and L. gasseri CECT5714 appear to be an efficient alternative for the treatment of lactational infectious mastitis during lactation.

Background: Breast milk is an important source of staphylococci and other bacterial groups to the infant gut. The objective of this work was to analyse the bacterial diversity in feces of breast-fed infants and to compare it with that of formula-fed ones. A total of 23 women and their respective infants (16 breast-fed and 7 formula-fed) participated in the study. The 16 women and their infants provided a sample of breast milk and feces, respectively, at days 7, 14, and 35. The samples were plated onto different culture media. Staphylococcal and enterococcal isolates were submitted to genetic profiling and to a characterization scheme, including detection of potential virulence traits and sensitivity to antibiotics.Results: The feeding practice had a significant effect on bacterial counts. A total of 1,210 isolates (489 from milk, 531 from breast-fed and 190 from formula-fed infants) were identified.Staphylococcus epidermidiswas the predominant species in milk and feces of breast-fed infants while it was less prevalent in those of formula fed-infants.Enterococcus faecaliswas the second predominant bacterial species among the fecal samples provided by the breast-fed infants but it was also present in all the samples from the formula-fed ones. The biofilm-relatedicaDgene and themecAgene were only detected in a low number of theS. epidermidisstrains. Several enterococcal isolates were also characterized and none of them contained thecylAor thevanABDEGantibiotic-resistance genes. All were sensitive to vancomycin.Conclusion: The presence ofS. epidermidisis a differential trait of the fecal microbiota of breast-fed infants. Globally, the staphyloccal isolates obtained from milk and feces of breast-fed infants contain a low number of virulence determinants and are sensitive to most of the antibiotics tested.

A new, coculture-inducible two-peptide bacteriocin named plantaricin NC8 (PLNC8) was isolated fromLactobacillus plantarumNC8 cultures which had been induced withLactococcus lactisMG1363 orPediococcus pentosaceusFBB63. This bacteriocin consists of two distinct peptides, named α and β, which were separated by C₂-C₁₈reverse-phase chromatography and whose complementary action is necessary for full plantaricin NC8 activity. N-terminal sequencing of both purified peptides showed 28 and 34 amino acids residues for PLNC8α and PLNC8β, respectively, which showed no sequence similarity to other known bacteriocins. Mass spectrometry analysis showed molecular masses of 3,587 Da (α) and 4,000 Da (β). The corresponding genes, designatedplNC8AandplNC8B, were sequenced, and their nucleotide sequences revealed that both peptides are produced as bacteriocin precursors of 47 and 55 amino acids, respectively, which include N-terminal leader sequences of the double-glycine type. The mature α and β peptides contain 29 and 34 amino acids, respectively. An open reading frame, orfC, which encodes a putative immunity protein was found downstream ofplNC8Band overlappingplNC8A. Upstream of the putative −35 region ofplNC8B, two direct repeats of 9 bp were identified, which agrees with the consensus sequence and structure of promoters of class II bacteriocin operons whose expression is dependent on an autoinduction mechanism.