Profiles of commensal and opportunistic bacteria in human milk from healthy donors in Taiwan

Abstract

Recent studies indicate that milk from healthy mothers may harbor potential probiotics. Nonetheless, the distribution of bacterial profiles in human milk samples in Taiwan is not fully understood. Therefore, with the aim to address this question, in this study, milk samples were collected from 33 healthy mothers (D1 to D33) visiting our hospital during a 6-month period. The milk microbiota was analyzed by a molecular approach (Illumina MiSeq sequencing). The results indicate that the milk samples have a unique profile and patterns of bacterial abundance levels. Moreover, in colostrum and transitional-milk samples, we detected 154 and 127 bacterial species, respectively, and these sets shared 42.6% of the bacterial species. The most common bacterial species among all milk samples were Staphylococcus epidermidis, Streptococcus lactarius, and Staphylococcus hominis, suggesting that the skin contamination route plays an important role in the composition of the milk microbiota. Nevertheless, four Lactobacillus species, Lactobacillus helveticus, Lactobacillus iners, Lactobacillus zeae, and Lactobacillus gasseri, were present in only 7 samples (21% prevalence), and bifidobacterial species were quite rare taxa among the present samples. The Staphylococcus aureus was detected in a total of 15 samples (45% prevalence), suggesting that this species may be commonly present in milk samples. In conclusion, each milk sample revealed a unique profile and patterns of bacterial abundance levels, and our data do not support the idea that lactobacilli and bifidobacteria are common and abundant in modern milk samples. Because none of the donors of the milk samples showed mastitis or any discomfort during the sampling process or at follow-up inspection, the microbiota of these milk samples is not likely to negatively affect its host. This study provides new information on the proportions of commensal bacteria in human milk in Taiwan.

Keywords: Bifidobacterium; Commensal bacteria; Human milk microbiota; Lactobacillus; Staphylococcus aureus.

Conflict of interest statement

Conflicts of interest

No conflict of interest exists.

Copyright © 2018. Published by Elsevier B.V.

Figures

Fig. 1

Bacterial genus composition in human milk. The bars show the proportion of each bacterial genus detected by 16S rRNA sequencing of milk samples from healthy donors (n = 33). Genera that represented less than 1% of all bacterial genera were grouped into an “others” category. profiles between the two milk types are still unknown, and this topic needs to be investigated further.

Fig. 2

Proportions of each bacterial genus in colostrum (n = 20) and transitional milk (n = 10). The relative abundance of all bacterial genera were determined using 16S rRNA gene amplicon sequencing. The proportion of each bacterial genus is indicated in a specific color. Only the nine most common bacterial genera are shown.

Fig. 3

Principal coordinate analysis based on the bacterial genera identified in milk samples. Percentages shown along the axes represent the proportions of dissimilarity. Each circle represents the 16S rRNA gene sequences from a sample. Different colors and shapes represent the three lactational stages. C: Colostrum (C1 to C20); T: transitional (T1 to T10); M: mature milk (M1 to M3).

Fig. 4

Bacterial species composition in human milk. The bars show the proportions of each bacterial species detected by 16S rRNA sequencing of milk samples from healthy donors (n = 33). Species that represented less than 1% of all bacterial species were grouped in an “others” category.

Fig. 5

Common and different bacterial genera and species between two milk types. Venn diagrams showing the number of bacterial genera (upper) or species (bottom) shared between or unique to two milk types, excluding bacterial genera or species present at an abundance of