Table 1. Bacterial diversity of human milk from healthy mothers analyzed by sequencing method

Reference	Study population	Sequencing method	Major taxa identified	Conclusion
Martin et al., 2003	- Spain	Cultured for LAB, RAPD analysis	LAB found in all milk samples, specifically Lactobacillus gasseri and Enterococcus faecium	HM can be an important source of LAB to the infant, and these bacteria have an endogenous origin.
	- n=8
	- 4 d postpartum
Collado et al., 2009	- Spain	qRTi-PCR	All samples contained Staphylococcus, Bifidobacterium, Lactobacillus, and Streptococcus	HM contains an abundance of bacterial DNA.
	- n=50
Hunt et al., 2011	- United States	Pyrosequencing	9 core genera OTUs present in all samples: Staphylococcus, Streptococcus, Strratia, Pseudomonas, Corynebacterium, Ralstonia, Propionibacterium, Sphingomonas, Bradyrhizobioum	HM contains a diverse and complex bacterial community.
	- n=16
	- ~22-26 postpartum
	- 3 samples from each subject
Cabrera-Rubio et al., 2012	- Finland	Pyrosequencing, qPCR	Weisella, Leuconostoc, Staphylococcus, Streptococcus, and Lactococcus predominant in colostrum; Leuconostoc, Weisella, Lactococcus, and Staphylococcus predominant in mature milk	HM microbiome changes over lactation stages and differs by maternal weight and delivery mode.
	-n=18
	-0~2 d, 1 mo, and 6 mo postpartum
Jost et al., 2013	- Switzerland	Cultrues, Sanger sequencing, 454-pyrosequencing, 16S rRNA gene sequencing	Predominant: Staphylococcus, Streptococcus, and Propionibacterium	HM may significantly influence infant gut colonization and immune system.
	-n=7
	-3~6 d, 9~14 d, and 25~30 d postpartum
Ward et al., 2013	- Canada	Illumina sequencing	Predominant: Pseudomonas, Staphylococcus, and Streptococcus	Diversity of bacterial may be beneficial.
	-n=1 (pooled milk from 10 women)
	-9~30 d postpartum
Urbaniak et al., 2016	- Canada	Illumina sequencing	Predominant: Firmicutes and Proteobacteria; at the genus level Staphylococcus, Enterobacteriaceae, Psedomonas followed by Streptococcus, Lactobacillus	HM contains a diverse population of bacteria.
	-n=39
	-6 d and onwards postpartum
Williams et al., 2017	- United States	High-throughput sequencing	Predominant: Firmicutes; at the genus level Streptococcus, Staphylococcus Relatively stable microbial communities within	HM produced by individual women.
	-n=21
	-2 d to 6 mo postpartum
	-9 samples from each subject
Biagi et al., 2017	- Italy	Illumina NGS	Predominant: Streptococcus, Staphylococcus, Bifidobacterium	HM may influence infant gut colonization and immune system.
	-n=36
	-20 d postpartum

HM, human milk; LAB, lactic acid bacteria; OUT, operational taxonomic unit; PCR, polymerase chain reaction; qPCR, quantitative polymerase chain reaction; qRTi, quantitative real time; RAPD, random amplified polymorphic DNA; rRNA, ribosomal RNA.