Abstract
Human milk is the optimal nutrition source for infants and contains a complex mix of bioactive compounds and microorganisms. When unavailable, pasteurized donor milk may be provided, ...particularly to preterm infants. Holder pasteurization (HP) is typically implemented in human milk banks to prevent pathogen transmission. Given the impact of heat on milk bioactives, ultraviolet-C irradiation (UV-C) is an alternative being explored and has demonstrated effective bactericidal activity. In addition to bacteria, milk contains viruses, including primarily bacteriophages (phages) and which likely influence the developing bacterial microbiome of infants. However, the effect of pasteurization on human milk phages is unknown. This study assessed the effect of HP and UV-C on titres of exogenous bacteriophages inoculated into human milk. Ten donor human milk samples were tested in parallel with water controls. Milk samples or water controls were inoculated to a final concentration of 1 × 104 PFU/mL (±1 log) each of a thermotolerant Escherichia coli phage (T4) and a thermosensitive Staphylococcus aureus phage (BYJ20) and subjected to HP and UV-C treatments. UV-C inactivated both phages within milk and water controls, however, HP was ineffective against the thermotolerant T4 phages. Initial data suggest that UV-C treatment may eliminate phage with potential to affect preterm infant gut colonization. Further studies should extend this to other phages.
Human milk pasteurization methods impact bacteriophage titres, with potential consequences for donor milk fed infants.
The oral cavity is home to the second most diverse microbiome in the human body. This community contributes to both oral and systemic health. Acquisition and development of the oral microbiome is a ...dynamic process that occurs over early life; however, data regarding longitudinal assembly of the infant oral microbiome is scarce. While numerous factors have been associated with the composition of the infant oral microbiome, early feeding practices (breastfeeding and the introduction of solids) appear to be the strongest determinants of the infant oral microbiome. In the present review, we draw together data on the maternal, infant, and environmental factors linked to the composition of the infant oral microbiome, with a focus on early nutrition. Given evidence that breastfeeding powerfully shapes the infant oral microbiome, the review explores potential mechanisms through which human milk components, including microbes, metabolites, oligosaccharides, and antimicrobial proteins, may interact with and shape the infant oral microbiome. Infancy is a unique period for the oral microbiome. By enhancing our understanding of oral microbiome assembly in early life, we may better support both oral and systemic health throughout the lifespan.
The composition of human milk is influenced by storage and processing practices. The effects of thawing and warming practices on human milk composition remain poorly studied despite their prevalence ...in home, research, and donor milk bank settings. This review comprehensively examines the impact of different thawing and warming methods on nutritional and bioactive human milk components. While some components such as carbohydrates and minerals remain stable under most typical thawing and warming conditions, others, such as fat, immune proteins, bacterial and human cells, and peptide amine hormones, are sensitive to warming. This review has identified that the data on the effects of milk thawing and warming is limited and often contradictory. Given that numerous important components of milk are diminished during cold storage, it is important that thawing and warming practices do not lead to further loss of or alterations to beneficial milk components. Further work in this field will facilitate greater standardization of thawing methods among researchers and underpin recommendations for thawing and warming of expressed milk for parents.
Analysis of the human milk microbiome is complicated by the presence of a variable quantity of fat. The fat fraction of human milk is typically discarded prior to analysis. It is assumed that all ...cells are pelleted out of human milk by high speed centrifugation; however, studies of bovine milk have reported that bacteria may remain trapped within the fat fraction. Here, the bacterial DNA profiles of the fat fraction and cell pellet of human milk (n = 10) were analysed. Human and bacterial DNA was consistently recovered from the fat fraction of human milk (average of 12.4% and 32.7%, respectively). Staphylococcus epidermidis was significantly more abundant in the cell pellet compared to the fat fraction (P = 0.038), and three low-abundance species (< 5% relative abundance) were recovered from one fraction only. However, inclusion of fat reduced the efficiency of DNA extraction by 39%. Culture-based methods were used to quantify the distribution of an exogenously added strain of Staphylococcus aureus in human milk fractions. S. aureus was consistently recovered from the fat fraction (average 28.9%). Bacterial DNA profiles generated from skim milk or cell pellets are not representative of the entire human milk microbiome. These data have critical implications for the design of future work in this field.
Although there has been limited application in the field to date, human milk omics research continues to gain traction. Human milk lipidomics and metabolomics research is particularly important, ...given the significance of milk lipids and metabolites for infant health. For researchers conducting compositional milk analyses, it is important to consider the origins of these compounds. The current review aims to provide a summary of the existing evidence on the sources of human milk lipids and small metabolites. Here, we describe five major sources of milk lipids and metabolites: de novo synthesis from mammary cells, production by the milk microbiota, dietary consumption, release from non-mammary tissue, and production by the gut microbiota. We synthesize the literature to provide evidence and understanding of these pathways in the context of mammary gland biology. We recommend future research focus areas to elucidate milk lipid and small metabolite synthesis and transport pathways. Better understanding of the origins of human milk lipids and metabolites is important to improve translation of milk omics research, particularly regarding the modulation of these important milk components to improve infant health outcomes.
Short chain fatty acids (SFCAs) are microbial metabolites produced in the gut upon fermentation of dietary fiber. These metabolites interact with the host immune system and can elicit epigenetic ...effects. There is evidence to suggest that SCFAs may play a role in the developmental programming of immune disorders and obesity, though evidence in humans remains sparse. Here we have quantified human milk (HM) SCFA levels in an international cohort of atopic and non-atopic mothers (
= 109). Our results demonstrate that human milk contains detectable levels of the SCFAs acetate, butyrate, and formate. Samples from atopic mothers had significantly lower concentrations of acetate and butyrate than those of non-atopic mothers. HM SCFA levels in atopic and non-atopic women also varied based on maternal country of residence (Australia, Japan, Norway, South Africa, USA). Reduced exposure to HM SCFA in early life may program atopy or overweight risk in breastfed infants.
Expression and cold storage of human milk is a common practice. Current guidelines for cold storage of expressed milk do not take into account the impact on the milk microbiome. Here, we investigated ...the impact of cold storage on viable bacterial populations in human milk. Freshly expressed milk samples (n = 10) were collected and analysed immediately, stored at 4 °C for four days, −20 °C for 2.25 months and 6 months, and −80 °C for 6 months. Samples were analysed using propidium monoazide (PMA; a cell viability dye) coupled with full-length 16S rRNA gene. An aliquot of each sample was additionally analysed without PMA to assess the impact of cold storage on the total DNA profile of human milk. Cold storage significantly altered the composition of both the viable microbiome and total bacterial DNA profile, with differences in the relative abundance of several OTUs observed across each storage condition. However, cold storage did not affect the richness nor diversity of the samples (PERMANOVA all p > 0.2). Storage of human milk under typical and recommended conditions results in alterations to the profile of viable bacteria, with potential implications for infant gut colonisation and infant health.
Human milk is a complex and variable ecosystem fundamental to the development of newborns. This study aimed to investigate relationships between human milk oligosaccharides (HMO) and human milk ...bacterial profiles and infant body composition. Human milk samples (
= 60) were collected at two months postpartum. Infant and maternal body composition was measured with bioimpedance spectroscopy. Human milk bacterial profiles were assessed using full-length 16S rRNA gene sequencing and 19 HMOs were quantitated using high-performance liquid chromatography. Relative abundance of human milk bacterial taxa were significantly associated with concentrations of several fucosylated and sialylated HMOs. Individual human milk bacteria and HMO intakes and concentrations were also significantly associated with infant anthropometry, fat-free mass, and adiposity. Furthermore, when data were stratified based on maternal secretor status, some of these relationships differed significantly among infants born to secretor vs non-secretor mothers. In conclusion, in this pilot study the human milk bacterial profile and HMO intakes and concentrations were significantly associated with infant body composition, with associations modified by secretor status. Future research designed to increase the understanding of the mechanisms by which HMO and human milk bacteria modulate infant body composition should include intakes in addition to concentrations.
Abstract
Human milk (HM) contains an incredible array of microorganisms. These likely contribute to the seeding of the infant gastrointestinal microbiome, thereby influencing infant immune and ...metabolic development and later-life health. Given the importance of the HM microbiota in this context, there has been an increase in research efforts to characterize this in different populations and in relation to different maternal and infant characteristics. However, despite a decade of intensive research, there remain several unanswered questions in this field. In this review, the “5 W+H” approach (who, what, when, where, why, and how) is used to comprehensively describe the composition, function, and origin of the HM microbiome. Here, existing evidence will be drawn together and critically appraised to highlight avenues for further research, both basic and applied. Perhaps the most interesting of these is the potential to modulate the HM microbiome using pre/probiotics or dietary interventions. Another exciting possibility is the personalization of donor milk for women with insufficient supply. By gaining a deeper understanding of the HM microbiome, opportunities to intervene to optimize infant and lifelong health may be identified.
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