Interrogation of Human Milk Oligosaccharide Fucosylation Patterns for Antimicrobial and Antibiofilm Trends in Group B Streptococcus

Dietary human milk oligosaccharides reduce allergic airway inflammation by modulating SCFAs level and ILC2 activity

Group 2 innate lymphoid cells (ILC2s) play a crucial role in the progression of asthma, yet the regulatory mechanisms modulating ILC2 responses in asthma remain underexplored. Human milk oligosaccharides (HMOs), vital non-nutritive components of breast milk, are known to significantly shape immune system development and influence the incidence of allergic diseases. However, their impact on ILC2-driven asthma is not fully understood. Our research reveals that dietary HMOs act as potent inhibitors of ILC2 responses and allergic airway inflammation. Treatment with 2'-fucosyllactose (2'-FL) and 6'-sialyllactose (6'-SL) significantly reduced ILC2-related airway inflammation induced by papain or Alternaria alternata in mice, evidenced by decreased eosinophil (EOS) infiltration and lower IL-5 and IL-13 levels in BALF. Notably, while ILC2 expresses HMO receptors, HMO did not act directly on ILC2 but potentially modulated their activity through alterations in gut microbiota derived SCFAs. HMO treatments alleviated airway inflammation in SCFA-dependent manners, with SCFA depletion or receptor blocking reversing these beneficial effects. This study reveals the potential of dietary HMOs in managing asthma through modulation of ILC2 activity and the gut-lung axis, proposing a new therapeutic avenue that utilises the immunomodulatory capacities of nutritional components to combat respiratory diseases.

Recent Progress in Physiological Significance and Biosynthesis of Lacto-N-triose II: Insights into a Crucial Biomolecule

Lacto-N-triose II (LNTri II), an important precursor for human milk oligosaccharide (HMOs) synthesis, has garnered significant attention due to its structural features and physiological properties. Composed of galactose (Gal), N-acetylglucosamine (GlcNAc), and glucose (Glc), with the chemical structure GlcNAcβ1,3Galβ1,4Glc, the distinctive structure of LNTri II confers various physiological functions such as promoting the growth of beneficial bacteria, regulating the infant immune system, and preventing certain gastrointestinal diseases. Extensive research efforts have been dedicated to elucidating efficient enzymatic synthesis pathways for LNTri II production, with particular emphasis on the transglycosylation activity of β-N-acetylhexosaminidases and the action of β-1,3-N-acetylglucosaminyltransferases. Additionally, metabolic engineering and cell factory approaches have been explored, harnessing the potential of engineered microbial hosts for the large-scale biosynthesis of LNTri II. This review summarizes the structure, derivatives, physiological effects, and biosynthesis of LNTri II.

Recent advances of 3-fucosyllactose in health effects and production

Human milk oligosaccharides (HMOs) have been recognized as gold standard for infant development. 3-Fucosyllactose (3-FL), being one of the Generally Recognized as Safe HMOs, represents a core trisaccharide within the realm of HMOs; however, it has received comparatively less attention in contrast to extensively studied 2'-fucosyllactose. The objective of this review is to comprehensively summarize the health effects of 3-FL, including its impact on gut microbiota proliferation, antimicrobial effects, immune regulation, antiviral protection, and brain maturation. Additionally, the discussion also covers the commercial application and regulatory approval status of 3-FL. Lastly, an organized presentation of large-scale production methods for 3-FL aims to provide a comprehensive guide that highlights current strategies and challenges in optimization.

Antimicrobial activity and structure-activity relationships of molecules containing mono- or di- or oligosaccharides: An update

Bacterial infections are the second leading cause of death worldwide, and the evolution and widespread distribution of antibiotic-resistance elements in bacterial pathogens exacerbate the threat crisis. Carbohydrates participate in bacterial infection, drug resistance and the process of host immune regulation. Numerous antimicrobials derived from carbohydrates or contained carbohydrate scaffolds that are conducive to an increase in pathogenic bacteria targeting, the physicochemical properties and druggability profiles. In the paper, according to the type and number of sugar residues contained in antimicrobial molecules collected from the literatures ranging from 2014 to 2024, the antimicrobial activities, action mechanisms and structure-activity relationships were delineated and summarized, for purpose to provide the guiding template to select the type and size of sugars in the design of oligosaccharide-based antimicrobials to fight the looming antibiotic resistance crisis.

Which is the optimal choice for neonates' formula or breast milk?

The incidence of prematurity has been increasing since the twenty-first century. Premature neonates are extremely vulnerable and require a rich supply of nutrients, including carbohydrates, proteins, docosahexaenoic acid (DHA), arachidonic acid (ARA) and others. Typical breast milk serves as the primary source for infants under six months old to provide these nutrients. However, depending on the individual needs of preterm infants, a more diverse and intricate range of nutrients may be necessary. This paper provides a comprehensive review of the current research progress on the physical and chemical properties, biological activity, function, and structure of breast milk, as well as explores the relationship between the main components of milk globular membrane and infant growth. Additionally, compare the nutritional composition of milk from different mammals and newborn milk powder, providing a comprehensive understanding of the differences in milk composition and detailed reference for meeting daily nutritional needs during lactation.

Antimicrobial Properties of Colostrum and Milk

The growing number of antibiotic resistance genes is putting a strain on the ecosystem and harming human health. In addition, consumers have developed a cautious attitude towards chemical preservatives. Colostrum and milk are excellent sources of antibacterial components that help to strengthen the immunity of the offspring and accelerate the maturation of the immune system. It is possible to study these important defenses of milk and colostrum, such as lactoferrin, lysozyme, immunoglobulins, oligosaccharides, etc., as biotherapeutic agents for the prevention and treatment of numerous infections caused by microbes. Each of these components has different mechanisms and interactions in various places. The compound's mechanisms of action determine where the antibacterial activity appears. The activation of the antibacterial activity of milk and colostrum compounds can start in the infant's mouth during lactation and continue in the gastrointestinal regions. These antibacterial properties possess potential for therapeutic uses. In order to discover new perspectives and methods for the treatment of bacterial infections, additional investigations of the mechanisms of action and potential complexes are required.

Breast Milk Oligosaccharides Contain Immunomodulatory Glucuronic Acid and LacdiNAc

Breast milk is abundant with functionalized milk oligosaccharides (MOs) to nourish and protect the neonate. Yet we lack a comprehensive understanding of the repertoire and evolution of MOs across Mammalia. We report ∼400 MO-species associations (>100 novel structures) from milk glycomics of nine mostly understudied species: alpaca, beluga whale, black rhinoceros, bottlenose dolphin, impala, L'Hoest's monkey, pygmy hippopotamus, domestic sheep, and striped dolphin. This revealed the hitherto unknown existence of the LacdiNAc motif (GalNAcβ1-4GlcNAc) in MOs of all species except alpaca, sheep, and striped dolphin, indicating the widespread occurrence of this potentially antimicrobial motif in MOs. We also characterize glucuronic acid-containing MOs in the milk of impala, dolphins, sheep, and rhinoceros, previously only reported in cows. We demonstrate that these GlcA-MOs exhibit potent immunomodulatory effects. Our study extends the number of known MOs by >15%. Combined with >1900 curated MO-species associations, we characterize MO motif distributions, presenting an exhaustive overview of MO biodiversity.

Age-dependent associations of human milk oligosaccharides with body size and composition up to 4 years of age

BACKGROUND

Human milk oligosaccharides (HMOs) are major components of human milk that may mediate its beneficial effects on infant growth.

OBJECTIVES

To investigate relationships between HMO concentrations in milk at 6 wk postpartum and anthropometry to 4 y of age in human milk-fed infants.

METHODS

Milk samples were collected from 292 mothers at 6 wk (median 6.0 wk; range 3.3, 11.1] postpartum in a longitudinal, population-derived cohort. Of the infants, 171 were exclusively human milk-fed to 3 mo of age and 127 to 6 mo. Concentrations of 19 HMOs were quantified using high-performance liquid chromatography. Maternal secretor status (n = 221 secretors) was determined from 2'-fucosyllactose (2'FL) concentration. We calculated z-scores for child weight, length, head circumference, summed triceps and subscapular skinfold thicknesses, and weight-for-length at 6 wk, 6 mo, 12 mo, and 4 y. We investigated associations of secretor status and each HMO measure with change from birth for each z-score using linear mixed-effects models.

RESULTS

Maternal secretor status was not associated with anthropometric z-scores up to 4 y of age. Several HMOs were associated with z-scores at 6 wk and 6 mo, predominantly within secretor status subgroups. Higher levels of 2'FL were associated with greater weight [β = 0.91 increase in z-score per SD increase log-2'FL, 95% CI (0.17, 1.65)] and length [β = 1.22, (0.25, 2.20)] in children born to secretor mothers, but not body composition measures. Higher lacto-N-tetraose was associated with greater weight [β = 0.22, (0.02, 0.41)] and length (β = 0.30, (0.07, 0.53)] among children born to nonsecretor mothers. Several HMOs were associated with anthropometric measures at 12 mo and 4 y of age.

CONCLUSIONS

Milk HMO composition at 6 wk postpartum is associated with several anthropometry measures up to 6 mo of age in a potential secretor status-specific manner, with largely different HMOs associating with anthropometry from 12 mo to 4 y of age.

Natural antimicrobial oligosaccharides in the food industry

An increase in the number of antibiotic resistance genes burdens the environment and affects human health. Additionally, people have developed a cautious attitude toward chemical preservatives. This attitude has promoted the search for new natural antimicrobial substances. Oligosaccharides from various sources have been studied for their antimicrobial and prebiotic effects. Antimicrobial oligosaccharides have several advantages such as being produced from renewable resources and showing antimicrobial properties similar to those of chemical preservatives. Their excellent broad-spectrum antibacterial properties are primarily because of various synergistic effects, including destruction of pathogen cell wall. Additionally, the adhesion of harmful microorganisms and the role of harmful factors may be reduced by oligosaccharides. Some natural oligosaccharides were also shown to stimulate the growth probiotic organisms. Therefore, antimicrobial oligosaccharides have the potential to meet food processing industry requirements in the future. The latest progress in research on the antimicrobial activity of different oligosaccharides is demonstrated in this review. The possible mechanism of action of these antimicrobial oligosaccharides is summarized with respect to their direct and indirect effects. Finally, the extended applications of oligosaccharides from the food source industry to food processing are discussed.

Recent advances on human milk oligosaccharide antimicrobial activity

Over the past century, human health has been enhanced by antimicrobial development. Following the deployment of the first antibiotics in the 1940s, bacterial resistance evolved and has increasingly outmaneuvered even the most promising antimicrobial agents. Accordingly, increased interest has been placed on alternative methods to circumvent antimicrobial resistance evolution. In the enclosed short review, we discuss the antimicrobial properties of human breast milk with a special emphasis on human milk oligosaccharides (HMOs). We recount studies across gram-negative and gram-positive pathogens, highlighting the usage of HMOs in promoting human health and wellness.

Human Milk Oligosaccharides as Potential Antibiofilm Agents: A Review

Surface-associated bacterial communities called biofilms are ubiquitous in nature. Biofilms are detrimental in medical settings due to their high tolerance to antibiotics and may alter the final pathophysiological outcome of many healthcare-related infections. Several innovative prophylactic and therapeutic strategies targeting specific mechanisms and/or pathways have been discovered and exploited in the clinic. One such emerging and original approach to dealing with biofilms is the use of human milk oligosaccharides (HMOs), which are the third most abundant solid component in human milk after lactose and lipids. HMOs are safe to consume (GRAS status) and act as prebiotics by inducing the growth and colonization of gut microbiota, in addition to strengthening the intestinal epithelial barrier, thereby protecting from pathogens. Moreover, HMOs can disrupt biofilm formation and inhibit the growth of specific microbes. In the present review, we summarize the potential of HMOs as antibacterial and antibiofilm agents and, hence, propose further investigations on using HMOs for new-age therapeutic interventions.

Non-Digestible Oligosaccharides: A Novel Treatment for Respiratory Infections?

Emerging antimicrobial resistance in respiratory infections requires novel intervention strategies. Non-digestible oligosaccharides (NDOs) are a diverse group of carbohydrates with broad protective effects. In addition to promoting the colonization of beneficial gut microbiota and maintaining the intestinal homeostasis, NDOs act as decoy receptors, effectively blocking the attachment of pathogens on host cells. NDOs also function as a bacteriostatic agent, inhibiting the growth of specific pathogenic bacteria. Based on this fact, NDOs potentiate the actions of antimicrobial drugs. Therefore, there is an increasing interest in characterizing the anti-infective properties of NDOs. This focused review provides insights into the mechanisms by which representative NDOs may suppress respiratory infections by targeting pathogens and host cells. We summarized the most interesting mechanisms of NDOs, including maintenance of gut microbiota homeostasis, interference with TLR-mediated signaling, anti-oxidative effects and bacterial toxin neutralization, bacteriostatic and bactericidal effects, and anti-adhesion or anti-invasive properties. A detailed understanding of anti-infective mechanisms of NDOs against respiratory pathogens may contribute to the development of add-on therapy or alternatives to antimicrobials.

The Diverse Antimicrobial Activities of Human Milk Oligosaccharides against Group B Streptococcus

Streptococcus agalactiae or Group B Streptococcus (GBS) is a Gram-positive bacterial pathobiont that is the etiological cause of severe perinatal infections. GBS can colonize the vagina of pregnant patients and invade tissues causing ascending infections of the gravid reproductive tract that lead to adverse outcomes including preterm birth, neonatal sepsis, and maternal or fetal demise. Additionally, transmission of GBS during labor or breastfeeding can also cause invasive infections of neonates and infants. However, human milk has also been shown to have protective effects against infection; a characteristic that is likely derived from antimicrobial and immunomodulatory properties of molecules that comprise human milk. Recent evidence suggests that human milk oligosaccharides (HMOs), short-chain sugars that comprise 8-20 % of breast milk, have antimicrobial and anti-biofilm activity against GBS and other bacterial pathogens. Additionally, HMOs have been shown to potentiate the activity of antibiotics against GBS. This review presents the most recent published work that studies the interaction between HMOs and GBS.

Proceedings from the 3rd International Conference on Microbiome Engineering

The human microbiome has been inextricably linked to multiple facets of human physiology. From an engineering standpoint, the ability to precisely control the composition and activity of the microbiome holds great promise for furthering our understanding of disease etiology and for new avenues of therapeutic and diagnostic agents. While the field of microbiome research is still in its infancy, growing engineering efforts are emerging to enable new studies in the microbiome and to rapidly translate these findings to microbiome‐based interventions. At the 3rd International Conference on Microbiome Engineering, leading experts in the field presented state‐of‐the‐art work in microbiome engineering, discussing probiotics, prebiotics, engineered microbes, microbially derived biomolecules, and bacteriophage.

Biology of human milk oligosaccharides: from Basic Science to Clinical Evidence

Human milk oligosaccharides (HMOs) have been researched by scientists for over 100 years, driven by the substantial evidence for the nutritional and health benefits of mother's milk. Yet research has truly bloomed during the last decade, thanks to the progress in biotechnology, which allowed the production of large amounts of bona fide HMOs. The availability of HMOs has been particularly crucial for the renewed interest in HMO research because of the low abundance or even absence of HMOs in farmed animal milk. This interest is reflected in the increasing number of original research publications and reviews on HMOs. Here, we provide an overview and critical discussion on structure function relations of HMOs that highlight why they are such interesting and important components of human milk. Clinical observations in breastfed infants backed by basic research from animal models provide guidance as to what physiological roles for HMOs are to be expected. From an evidence-based nutrition viewpoint, we discuss the current data supporting clinical relevance of specific HMOs based on randomized placebo controlled clinical intervention trials in formula-fed infants. This article is protected by copyright. All rights reserved.

Polysaccharides to combat viruses (Covid-19) and microbes: New updates

COVID-19, which is speedily distributed across the world and presents a significant challenge to public health, is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Following MERS coronavirus (MERS-CoV) and SARS, this is the third severe coronavirus outbreak in less than 20 years. To date, there are no exact agents and vaccines available for the treatment of COVID-19 that are clinically successful. Antimicrobial medications are effective in controlling infectious diseases. However, the extensive use of antibiotics makes microbes more resistant to drugs and demands novel bioactive agents' development. Polysaccharides are currently commonly used in the biomedical and pharmaceutical industries for their remarkable applications. Polysaccharides appear to have a wide range of anti-virus (anti-coronavirus) and antimicrobial applications. Polysaccharides are able to induce bacterial cell membrane disruption as they demonstrate potency in binding onto the surfaces of microbial cells. Here, the antiviral mechanisms of such polysaccharides and their success in the application of antiviral infections are reviewed. Additionally, this report provides a summary of current advancements of well-recognized polysaccharides as antimicrobial and anti-biofilm agents.

Human Milk Oligosaccharides Reduce Murine Group B Streptococcus Vaginal Colonization with Minimal Impact on the Vaginal Microbiota

Group B Streptococcus (GBS) colonizes the vaginal mucosa of a significant percentage of healthy women and is a leading cause of neonatal bacterial infections. Currently, pregnant women are screened in the last month of pregnancy, and GBS-positive women are given antibiotics during parturition to prevent bacterial transmission to the neonate. Recently, human milk oligosaccharides (HMOs) isolated from breastmilk were found to inhibit GBS growth and biofilm formation in vitro, and women that make certain HMOs are less likely to be vaginally colonized with GBS. Using in vitro human vaginal epithelial cells and a murine vaginal colonization model, we tested the impact of HMO treatment on GBS burdens and the composition of the endogenous microbiota by 16S rRNA amplicon sequencing. HMO treatment reduced GBS vaginal burdens in vivo with minimal alterations to the vaginal microbiota. HMOs displayed potent inhibitory activity against GBS in vitro, but HMO pretreatment did not alter adherence of GBS or the probiotic Lactobacillus rhamnosus to human vaginal epithelial cells. In addition, disruption of a putative GBS glycosyltransferase (Δsan_0913) rendered the bacterium largely resistant to HMO inhibition in vitro and in vivo but did not compromise its adherence, colonization, or biofilm formation in the absence of HMOs. We conclude that HMOs are a promising therapeutic bioactive to limit GBS vaginal colonization with minimal impacts on the vaginal microenvironment.

IMPORTANCE During pregnancy, GBS ascension into the uterus can cause fetal infection or preterm birth. In addition, GBS exposure during labor creates a risk of serious disease in the vulnerable newborn and mother postpartum. Current recommended prophylaxis consists of administering broad-spectrum antibiotics to GBS-positive mothers during labor. Although antibiotics have significantly reduced GBS neonatal disease, there are several unintended consequences, including altered neonatal gut bacteria and increased risk for other types of infection. Innovative preventions displaying more targeted antimicrobial activity, while leaving the maternal microbiota intact, are thus appealing. Using a mouse model, we found that human milk oligosaccharides (HMOs) reduce GBS burdens without perturbing the vaginal microbiota. We conclude that HMOs are a promising alternative to antibiotics to reduce GBS neonatal disease.

Distinct fermentation of human milk oligosaccharides 3-FL and LNT2 and GOS/inulin by infant gut microbiota and impact on adhesion of Lactobacillus plantarum WCFS1 to gut epithelial cells

Human milk oligosaccharides (hMOs) are unique bioactive components in human milk. 3-Fucosyllactose (3-FL) is an abundantly present hMO that can be produced in sufficient amounts to allow application in infant formula. Lacto-N-triaose II (LNT2) can be obtained by acid hydrolysis of lacto-N-neotetraose (LNnT). Both 3-FL and LNT2 have been shown to have health benefits, but their impact on infant microbiota composition and microbial metabolic products such as short-chain fatty acids (SCFAs) is unknown. To gain more insight in fermentability, we performed in vitro fermentation studies of 3-FL and LNT2 using pooled fecal microbiota from 12-week-old infants. The commonly investigated galacto-oligosaccharides (GOS)/inulin (9 : 1) served as control. Compared to GOS/inulin, we observed a delayed utilization of 3-FL, which was utilized at 60.3% after 36 h of fermentation, and induced the gradual production of acetic acid and lactic acid. 3-FL specifically enriched bacteria of Bacteroides and Enterococcus genus. LNT2 was fermented much faster. After 14 h of fermentation, 90.1% was already utilized, and production of acetic acid, succinic acid, lactic acid and butyric acid was observed. LNT2 specifically increased the abundance of Collinsella, as well as Bifidobacterium. The GOS present in the GOS/inulin mixture was completely fermented after 14 h, while for inulin, only low DP was rapidly utilized after 14 h. To determine whether the fermentation might lead to enhanced colonization of commensal bacteria to gut epithelial cells, we investigated adhesion of the commensal Lactobacillus plantarum WCFS1 to Caco-2 cells. The fermentation digesta of LNT2 collected after 14 h, 24 h, and 36 h, and GOS/inulin after 24 h of fermentation significantly increased the adhesion of L. plantarum WCFS1 to Caco-2 cells, while 3-FL had no such effect. Our findings illustrate that fermentation of hMOs is very structure-dependent and different from the commonly applied GOS/inulin, which might lead to differential potencies to stimulate adhesion of commensal cells to gut epithelium and consequent microbial colonization. This knowledge might contribute to the design of tailored infant formulas containing specific hMO molecules to meet the need of infants during the transition from breastfeeding to formula.

Antibiofilm Activity of Human Milk Oligosaccharides against Multidrug Resistant and Susceptible Isolates of Acinetobacter baumannii

Acinetobacter baumannii is a serious threat to human health, per the Centers for Disease Control and Prevention's latest threat assessment. A. baumannii is a Gram-negative opportunistic bacterial pathogen that causes severe community and nosocomial infections in immunocompromised patients. Treatment of these infections is confounded by the emergence of multi- and pan-drug resistant strains of A. baumannii. A. baumannii colonizes abiotic and biotic surfaces and evades antimicrobial challenges by forming biofilms, which are three-dimensional architectural structures of cells adhered to a substrate and encased in an extracellular matrix comprised of polymeric substances such as polysaccharides, proteins, and DNA. Biofilm-inhibiting compounds have recently gained attention as a chemotherapeutic strategy to prevent or disperse A. baumannii biofilms and restore the utility of traditional antimicrobial strategies. Recent work indicates that human milk oligosaccharides (HMOs) have potent antibacterial and biofilm-inhibiting properties. We sought to test the utility of HMOs against a bank of clinical isolates of A. baumannii to ascertain changes in bacterial growth or biofilm formation. Our results indicate that out of 18 strains tested, 14 were susceptible to the antibiofilm activities of HMOs, and that the potent antibiofilm activity was observed in strains isolated from diverse anatomical sites, disease manifestations, and across antibiotic-resistant and susceptible strains.

Multifunctional Benefits of Prevalent HMOs: Implications for Infant Health

Breastfeeding is the best source of nutrition during infancy and is associated with a broad range of health benefits. However, there remains a significant and persistent need for innovations in infant formula that will allow infants to access a wider spectrum of benefits available to breastfed infants. The addition of human milk oligosaccharides (HMOs) to infant formulas represents the most significant innovation in infant nutrition in recent years. Although not a direct source of calories in milk, HMOs serve as potent prebiotics, versatile anti-infective agents, and key support for neurocognitive development. Continuing improvements in food science will facilitate production of a wide range of HMO structures in the years to come. In this review, we evaluate the relationship between HMO structure and functional benefits. We propose that infant formula fortification strategies should aim to recapitulate a broad range of benefits to support digestive health, immunity, and cognitive development associated with HMOs in breastmilk. We conclude that acetylated, fucosylated, and sialylated HMOs likely confer important health benefits through multiple complementary mechanisms of action.

Antimicrobial Activities of Alginate and Chitosan Oligosaccharides Against Staphylococcus aureus and Group B Streptococcus

The bacterial pathogens Streptococcus agalactiae (GBS) and Staphylococcus aureus (S. aureus) cause serious infections in humans and animals. The emergence of antibiotic-resistant isolates and bacterial biofilm formation entails the urge of novel treatment strategies. Recently, there is a profound scientific interest in the capabilities of non-digestible oligosaccharides as antimicrobial and anti-biofilm agents as well as adjuvants in antibiotic combination therapies. In this study, we investigated the potential of alginate oligosaccharides (AOS) and chitosan oligosaccharides (COS) as alternative for, or in combination with antibiotic treatment. AOS (2-16%) significantly decreased GBS V growth by determining the minimum inhibitory concentration. Both AOS (8 and 16%) and COS (2-16%) were able to prevent biofilm formation by S. aureus wood 46. A checkerboard biofilm formation assay demonstrated a synergistic effect of COS and clindamycin on the S. aureus biofilm formation, while AOS (2 and 4%) were found to sensitize GBS V to trimethoprim. In conclusion, AOS and COS affect the growth of GBS V and S. aureus wood 46 and can function as anti-biofilm agents. The promising effects of AOS and COS in combination with different antibiotics may offer new opportunities to combat antimicrobial resistance.

Synthesis as an Expanding Resource in Human Milk Science

Few classes of natural products rival the structural audacity of oligosaccharides. Their complexity, however, has stood as an immense roadblock to translational research, as access to homogeneous material from nature is challenging. Thus, while carbohydrates are critical to the myriad functional and structural aspects of the biological sciences, their behavior is largely descriptive. This challenge presents an attractive opportunity for synthetic chemistry, particularly in the area of human milk science. First, there is an inordinate need for synthesizing homogeneous human milk oligosaccharides (HMOs). Superimposed on this goal is the mission of conducting syntheses at scale to enable animal studies. Herein, we present a personalized rumination of our involvement, and that of our colleagues, which has led to the synthesis and characterization of HMOs and mechanistic probes. Along the way, we highlight chemical, chemoenzymatic, and synthetic biology based approaches. We close with a discussion on emergent challenges and opportunities for synthesis, broadly defined, in human milk science.

Digestion, fermentation, and pathogen anti-adhesive properties of the hMO-mimic di-fucosyl-β-cyclodextrin

Human milk is widely acknowledged as the best food for infants, and that is not just because of nutritional features. Human milk also contains a plethora of bioactive molecules, including a large set of human milk oligosaccharides (hMOs). Especially fucosylated hMOs have received attention for their anti-adhesive effects on pathogens, preventing attachment to the intestine and infection. Because hMOs are generally challenging to produce in sufficient quantities to study and ultimately apply in (medical) infant formula, novel compounds that are inspired by hMO structures (so-called "mimics") are interesting compounds to produce and evaluate for their biological effects. Here we present our thorough study into the digestion, fermentation and anti-adhesive capacity of the novel compound di-fucosyl-β-cyclodextrin (DFβCD), which was inspired by the molecular structures of hMOs. We establish that DFβCD is not digested by α-amylase and also resistant to fermentation by microbial enzymes from a 9 month-old infant inoculum. In addition, we reveal that DFβCD blocks adhesion of enterotoxigenic E. coli (ETEC) to Caco-2 cells, especially when DFβCD is pre-incubated with ETEC prior to addition to the Caco-2 cells. This suggests that DFβCD functions through a decoy effect. We expect that our results inspire the generation and biological evaluation of other fucosylated hMOs and mimics, to obtain a comprehensive overview of the anti-adhesive power of fucosylated glycans.

Prospecting Human Milk Oligosaccharides as a Defense Against Viral Infections

In addition to providing maximal nutritional value for neonatal growth and development, human milk functions as an early defense mechanism against invading pathogens. Human milk oligosaccharides (HMOs), which are abundant in human milk, are a diverse group of heterogeneous carbohydrates with wide ranging protective effects. In addition to promoting the colonization of beneficial intestinal flora, HMOs serve as decoy receptors, effectively blocking the attachment of pathogenic bacteria. HMOs also function as bacteriostatic agents, inhibiting the growth of gram-positive bacteria. Based on this precedence, an emerging area in the field has focused on characterizing the antiviral properties of HMOs. Indeed, HMOs have been evaluated as antiviral agents, with many possessing activity against life-threatening infections. This targeted review provides insight into the known glycan-binding interactions between select HMOs and influenza, rotavirus, respiratory syncytial virus, human immunodeficiency virus, and norovirus. Additionally, we review the role of HMOs in preventing necrotizing enterocolitis, an intestinal disease linked to viral infections. We close with a discussion of what is known broadly regarding human milk oligosaccharides and their interactions with coronaviruses.

In Love with Shaping You-Influential Factors on the Breast Milk Content of Human Milk Oligosaccharides and Their Decisive Roles for Neonatal Development

Human milk oligosaccharides (HMOs) are structurally versatile sugar molecules constituting the third major group of soluble components in human breast milk. Based on the disaccharide lactose, the mammary glands of future and lactating mothers produce a few hundreds of different HMOs implicating that their overall anabolism utilizes rather high amounts of energy. At first sight, it therefore seems contradictory that these sugars are indigestible for infants raising the question of why such an energy-intensive molecular class evolved. However, in-depth analysis of their molecular modes of action reveals that Mother Nature created HMOs for neonatal development, protection and promotion of health. This is not solely facilitated by HMOs in their indigestible form but also by catabolites that are generated by microbial metabolism in the neonatal gut additionally qualifying HMOs as natural prebiotics. This narrative review elucidates factors influencing the HMO composition as well as physiological roles of HMOs on their way through the infant body and within the gut, where a major portion of HMOs faces microbial catabolism. Concurrently, this work summarizes in vitro, preclinical and observational as well as interventional clinical studies that analyzed potential health effects that have been demonstrated by or were related to either human milk-derived or synthetic HMOs or HMO fractions.

Leveraging Stereoelectronic Effects in Biofilm Eradication: Synthetic β-Amino Human Milk Oligosaccharides Impede Microbial Adhesion As Observed by Scanning Electron Microscopy

Alongside Edward, Lemieux was among the earliest researchers studying negative hyperconjugation (i.e., the anomeric effect) or the preference for gauche conformations about the C1-O5 bond in carbohydrates. Lemieux also studied an esoteric, if not controversial, theory known as the reverse anomeric effect (RAE). This theory is used to rationalize scenarios where predicted anomeric stabilization does not occur. One such example is the Kochetkov amination where reducing end amines exist solely as the β-anomer. Herein, we provide a brief account of Lemieux's contributions to the field of stereoelectronics and apply this knowledge toward the synthesis of β-amino human milk oligosaccharides (βΑ-HMOs). These molecules were evaluated for their ability to inhibit growth and biofilm production in Group B Streptococcus (GBS) and Staphylococcus aureus. While the parent HMOs lacked antimicrobial and antibiofilm activity, their β-amino derivatives significantly inhibited biofilm formation in both species. Field emission gun-scanning single electron microscopy (FEG-SEM) revealed that treatment with β-amino HMOs significantly inhibits bacterial adherence and eliminates the ability of both microbes to form biofilms.

A nonenzymatic method for cleaving polysaccharides to yield oligosaccharides for structural analysis

Polysaccharides are the most abundant biomolecules in nature, but are the least understood in terms of their chemical structures and biological functions. Polysaccharides cannot be simply sequenced because they are often highly branched and lack a uniform structure. Furthermore, large polymeric structures cannot be directly analyzed by mass spectrometry techniques, a problem that has been solved for polynucleotides and proteins. While restriction enzymes have advanced genomic analysis, and trypsin has advanced proteomic analysis, there has been no equivalent enzyme for universal polysaccharide digestion. We describe the development and application of a chemical method for producing oligosaccharides from polysaccharides. The released oligosaccharides are characterized by advanced liquid chromatography-mass spectrometry (LC-MS) methods with high sensitivity, accuracy and throughput. The technique is first used to identify polysaccharides by oligosaccharide fingerprinting. Next, the polysaccharide compositions of food and feces are determined, further illustrating the utility of technique in food and clinical studies.

Like mother, like microbe: human milk oligosaccharide mediated microbiome symbiosis

Starting shortly after parturition, and continuing throughout our lifetime, the gut microbiota coevolves with our metabolic and neurological programming. This symbiosis is regulated by a complex interplay between the host and environmental factors, including diet and lifestyle. Not surprisingly, the development of this microbial community is of critical importance to health and wellness. In this targeted review, we examine the gut microbiome from birth to 2 years of age to characterize the role human milk oligosaccharides play in early formation of microbial flora.

Anti-Pathogenic Functions of Non-Digestible Oligosaccharides In Vitro

Non-digestible oligosaccharides (NDOs), complex carbohydrates that resist hydrolysis by salivary and intestinal digestive enzymes, fulfill a diversity of important biological roles. A lot of NDOs are known for their prebiotic properties by stimulating beneficial bacteria in the intestinal microbiota. Human milk oligosaccharides (HMOs) represent the first prebiotics that humans encounter in life. Inspired by these HMO structures, chemically-produced NDO structures (e.g., galacto-oligosaccharides and chito-oligosaccharides) have been recognized as valuable food additives and exert promising health effects. Besides their apparent ability to stimulate beneficial microbial species, oligosaccharides have shown to be important inhibitors of the development of pathogenic infections. Depending on the type and structural characteristics, oligosaccharides can exert a number of anti-pathogenic effects. The most described effect is their ability to act as a decoy receptor, thereby inhibiting adhesion of pathogens. Other ways of pathogenic inhibition, such as interference with pathogenic cell membrane and biofilm integrity and DNA transcription, are less investigated, but could be equally impactful. In this review, a comprehensive overview of In vitro anti-pathogenic properties of different NDOs and associated pathways are discussed. A framework is created categorizing all anti-pathogenic effects and providing insight into structural necessities for an oligosaccharide to exert one of these effects.

Human Milk Oligosaccharides Modulate the Risk for Preterm Birth in a Microbiome-Dependent and -Independent Manner

The causes for preterm birth (PTB) often remain elusive. We investigated whether circulating human milk oligosaccharides (HMOs) might be involved in modulating urinary and vaginal microbiome promoting or preventing PTB. We identified here HMOs and key microbial taxa associated with indicators of PTB. Based on our results, we propose two models for how HMOs might modulate risk for PTB: (i) by changes in HMOs associated with sterile inflammation (microbiome-independent) and (ii) by HMO-driven shifts in microbiome (microbiome-dependent). Our findings will guide current efforts to better predict the risk for PTB in seemingly healthy pregnant women and also provide appropriate preventive strategies.

Preterm birth (PTB) is one of the leading causes of neonatal mortality. The causes for spontaneous PTB are multifactorial and often remain unknown. In this study, we tested the hypothesis that human milk oligosaccharides (HMOs) in blood and urine modulate the maternal urinary and vaginal microbiome and influence the risk for PTB. We analyzed the vaginal and urinary microbiome of a cross-sectional cohort of women with or without preterm labor and correlated our findings with measurements of metabolites and HMOs in urine and blood. We identified several microbial signatures, such as Lactobacillus jensenii, L. gasseri, Ureaplasma sp., and Gardnerella sp., associated with a short cervix, PTB, and/or preterm contractions. In addition, we observed associations between sialylated HMOs, in particular 3′-sialyllactose, with PTB, short cervix, and increased inflammation and confirmed an influence of HMOs on the microbiome profile. Since they identify serum and urinary HMOs and several key microorganisms associated with PTB, our findings point at two distinct processes modulating the risk for PTB. One process seems to be driven by sterile inflammation, characterized by increased concentrations of sialylated HMOs in serum. Another process might be microbiome mediated and potentially associated with specific HMO signatures in urine. Our results support current efforts to improve diagnostics and therapeutic strategies in PTB.

IMPORTANCE The causes for preterm birth (PTB) often remain elusive. We investigated whether circulating human milk oligosaccharides (HMOs) might be involved in modulating urinary and vaginal microbiome promoting or preventing PTB. We identified here HMOs and key microbial taxa associated with indicators of PTB. Based on our results, we propose two models for how HMOs might modulate risk for PTB: (i) by changes in HMOs associated with sterile inflammation (microbiome-independent) and (ii) by HMO-driven shifts in microbiome (microbiome-dependent). Our findings will guide current efforts to better predict the risk for PTB in seemingly healthy pregnant women and also provide appropriate preventive strategies.

Immunomodulation by Human Milk Oligosaccharides: The Potential Role in Prevention of Allergic Diseases

The prevalence and incidence of allergic diseases is rising and these diseases have become the most common chronic diseases during childhood in Westernized countries. Early life forms a critical window predisposing for health or disease. Therefore, this can also be a window of opportunity for allergy prevention. Postnatally the gut needs to mature, and the microbiome is built which further drives the training of infant's immune system. Immunomodulatory components in breastmilk protect the infant in this crucial period by; providing nutrients that contain substrates for the microbiome, supporting intestinal barrier function, protecting against pathogenic infections, enhancing immune development and facilitating immune tolerance. The presence of a diverse human milk oligosaccharide (HMOS) mixture, containing several types of functional groups, points to engagement in several mechanisms related to immune and microbiome maturation in the infant's gastrointestinal tract. In recent years, several pathways impacted by HMOS have been elucidated, including their capacity to; fortify the microbiome composition, enhance production of short chain fatty acids, bind directly to pathogens and interact directly with the intestinal epithelium and immune cells. The exact mechanisms underlying the immune protective effects have not been fully elucidated yet. We hypothesize that HMOS may be involved in and can be utilized to provide protection from developing allergic diseases at a young age. In this review, we highlight several pathways involved in the immunomodulatory effects of HMOS and the potential role in prevention of allergic diseases. Recent studies have proposed possible mechanisms through which HMOS may contribute, either directly or indirectly, via microbiome modification, to induce oral tolerance. Future research should focus on the identification of specific pathways by which individual HMOS structures exert protective actions and thereby contribute to the capacity of the authentic HMOS mixture in early life allergy prevention.

Structural features, interaction with the gut microbiota and anti-tumor activity of oligosaccharides

Some oligosaccharides are regarded as biological constituents with benefits to human health in an indirect way. They enter the intestinal tract to be fermented by the gut microbiota, causing changes in the abundance and composition of the gut microbiota and producing fermentation products such as short-chain fatty acids (SCFAs). In this review, the structural features and biological activities of eight common natural oligosaccharides were summarized, including human milk oligosaccharides (HMOS), xylo-oligosaccharides (XOS), arabinoxylo-oligosaccharides (AXOS), isomaltooligosaccharides (IMOS), chitin oligosaccharides (NACOS), mannan-oligosaccharides (MOS), galacto-oligosaccharides (GOS) and fructo-oligosaccharides (FOS). Furthermore, XOS were selected to explain the anti-tumor mechanism mediated by gut microbiota. The review aims to reveal primary structural features of natural functional oligosaccharides related to the biological activities and also provide an explanation of the anti-tumor activity of functional oligosaccharides mediated by the gut microbiota.

The Impact of Dietary Fucosylated Oligosaccharides and Glycoproteins of Human Milk on Infant Well-Being

Apart from optimal nutritional value, human milk is the feeding strategy to support the immature immunological system of developing newborns and infants. The most beneficial dietary carbohydrate components of breast milk are human milk oligosaccharides (HMOs) and glycoproteins (HMGs), involved in both specific and nonspecific immunity. Fucosylated oligosaccharides represent the largest fraction of human milk oligosaccharides, with the simplest and the most abundant being 2'-fucosyllactose (2'FL). Fucosylated oligosaccharides, as well as glycans of glycoproteins, as beneficial dietary sugars, elicit anti-adhesive properties against fucose-dependent pathogens, and on the other hand are crucial for growth and metabolism of beneficial bacteria, and in this aspect participate in shaping a healthy microbiome. Well-documented secretor status related differences in the fucosylation profile of HMOs and HMGs may play a key but underestimated role in assessment of susceptibility to fucose-dependent pathogen infections, with a potential impact on applied clinical procedures. Nevertheless, due to genetic factors, about 20% of mothers do not provide their infants with beneficial dietary carbohydrates such as 2'-FL and other α1,2-fucosylated oligosaccharides and glycans of glycoproteins, despite breastfeeding them. The lack of such structures may have important implications for a wide range of aspects of infant well-being and healthcare. In light of the above, some artificial mixtures used in infant nutrition are supplemented with 2'-FL to more closely approximate the unique composition of maternal milk, including dietary-derived fucosylated oligosaccharides and glycoproteins.

A Solution to Antifolate Resistance in Group B Streptococcus: Untargeted Metabolomics Identifies Human Milk Oligosaccharide-Induced Perturbations That Result in Potentiation of Trimethoprim

Adjuvants can be used to potentiate the function of antibiotics whose efficacy has been reduced by acquired or intrinsic resistance. In the present study, we discovered that human milk oligosaccharides (HMOs) sensitize strains of group B Streptococcus (GBS) to trimethoprim (TMP), an antibiotic to which GBS is intrinsically resistant. Reductions in the MIC of TMP reached as high as 512-fold across a diverse panel of isolates. To better understand HMOs' mechanism of action, we characterized the metabolic response of GBS to HMO treatment using ultrahigh-performance liquid chromatography-high-resolution tandem mass spectrometry (UPLC-HRMS/MS) analysis. These data showed that when challenged by HMOs, GBS undergoes significant perturbations in metabolic pathways related to the biosynthesis and incorporation of macromolecules involved in membrane construction. This study represents reports the metabolic characterization of a cell that is perturbed by HMOs.IMPORTANCE Group B Streptococcus is an important human pathogen that causes serious infections during pregnancy which can lead to chorioamnionitis, funisitis, premature rupture of gestational membranes, preterm birth, neonatal sepsis, and death. GBS is evolving antimicrobial resistance mechanisms, and the work presented in this paper provides evidence that prebiotics such as human milk oligosaccharides can act as adjuvants to restore the utility of antibiotics.

Bioorthogonal human milk oligosaccharide probes for antimicrobial target identification within Streptococcus agalactiae

Human milk oligosaccharides (HMOs) are a structurally diverse class of carbohydrates that possess strong antibacterial activity against Streptococcus agalactiae (Group B Strep, GBS). This work highlights the design, synthesis, and retained biological activity of several HMO bioorthogonal probes within GBS, a first in class advance. The use of such probes will assist in identifying HMO-protein interactions within GBS and may be broadly applicable in researching HMO cellular targets within a variety of biological systems. Finally, this strategy is highly amenable to other oligosaccharide scaffolds, requiring minimal synthetic transformations and chemical perturbation.

Human Milk Oligosaccharide, Phospholipid, and Ganglioside Concentrations in Breast Milk from United Arab Emirates Mothers: Results from the MISC Cohort

Human milk oligosaccharides (HMOs), phospholipids (PLs), and gangliosides (GAs) are components of human breast milk that play important roles in the development of the rapidly growing infant. The differences in these components in human milk from the United Arab Emirates (UAE) were studied in a cross-sectional trial. High-performance liquid chromatography‒mass spectrometry was used to determine HMO, PL, and GA concentrations in transitional (5-15 days) and mature (at 6 months post-partum) breast milk of mothers of the United Arab Emirates (UAE). The results showed that the average HMO (12 species), PL (7 species), and GA (2 species) concentrations quantified in the UAE mothers' transitional milk samples were (in mg/L) 8204 ± 2389, 269 ± 89, and 21.18 ± 11.46, respectively, while in mature milk, the respective concentrations were (in mg/L) 3905 ± 1466, 220 ± 85, and 20.18 ± 9.75. The individual HMO concentrations measured in this study were all significantly higher in transitional milk than in mature milk, except for 3 fucosyllactose, which was higher in mature milk. In this study, secretor and non-secretor phenotype mothers showed no significant difference in the total HMO concentration. For the PL and GA components, changes in the individual PL and GA species distribution was observed between transitional milk and mature milk. However, the changes were within the ranges found in human milk from other regions.

Temporal development of the infant gut microbiome

The majority of organisms that inhabit the human body reside in the gut. Since babies are born with an immature immune system, they depend on a highly synchronized microbial colonization process to ensure the correct microbes are present for optimal immune function and development. In a balanced microbiome, symbiotic and commensal species outcompete pathogens for resources. They also provide a protective barrier against chemical signals and toxic metabolites. In this targeted review we will describe factors that influence the temporal development of the infant microbiome, including the mode of delivery and gestational age at birth, maternal and infant perinatal antibiotic infusions, and feeding method-breastfeeding versus formula feeding. We will close by discussing wider environmental pressures and early intimate contact, particularly between mother and child, as they play a pivotal role in early microbial acquisition and community succession in the infant.

Diet-Microbe-Host Interactions That Affect Gut Mucosal Integrity and Infection Resistance

The gastrointestinal tract microbiome plays a critical role in regulating host innate and adaptive immune responses against pathogenic bacteria. Disease associated dysbiosis and environmental induced insults, such as antibiotic treatments can lead to increased susceptibility to infection, particularly in a hospital setting. Dietary intervention is the greatest tool available to modify the microbiome and support pathogen resistance. Some dietary components can maintain a healthy disease resistant microbiome, whereas others can contribute to an imbalanced microbial population, impairing intestinal barrier function and immunity. Characterizing the effects of dietary components through the host-microbe axis as it relates to gastrointestinal health is vital to provide evidence-based dietary interventions to mitigate infections. This review will cover the effect of dietary components (carbohydrates, fiber, proteins, fats, polyphenolic compounds, vitamins, and minerals) on intestinal integrity and highlight their ability to modulate host-microbe interactions as to improve pathogen resistance.

Synthesis of Human Milk Oligosaccharides: Protein Engineering Strategies for Improved Enzymatic Transglycosylation

Human milk oligosaccharides (HMOs) signify a unique group of oligosaccharides in breast milk, which is of major importance for infant health and development. The functional benefits of HMOs create an enormous impetus for biosynthetic production of HMOs for use as additives in infant formula and other products. HMO molecules can be synthesized chemically, via fermentation, and by enzymatic synthesis. This treatise discusses these different techniques, with particular focus on harnessing enzymes for controlled enzymatic synthesis of HMO molecules. In order to foster precise and high-yield enzymatic synthesis, several novel protein engineering approaches have been reported, mainly concerning changing glycoside hydrolases to catalyze relevant transglycosylations. The protein engineering strategies for these enzymes range from rationally modifying specific catalytic residues, over targeted subsite -1 mutations, to unique and novel transplantations of designed peptide sequences near the active site, so-called loop engineering. These strategies have proven useful to foster enhanced transglycosylation to promote different types of HMO synthesis reactions. The rationale of subsite -1 modification, acceptor binding site matching, and loop engineering, including changes that may alter the spatial arrangement of water in the enzyme active site region, may prove useful for novel enzyme-catalyzed carbohydrate design in general.

Mother Knows Best: Deciphering the Antibacterial Properties of Human Milk Oligosaccharides

This Account describes the risky proposition of organizing a multidisciplinary team to interrogate a challenging problem in chemical biology: characterizing how human milk, at the molecular level, protects infants from infectious diseases. At the outset, our initial hypothesis was that human milk oligosaccharides (HMOs) possess antimicrobial and antivirulence activities. Early on, we discovered that HMOs do indeed modulate bacterial growth and biofilm production for numerous bacterial pathogens. In light of this discovery, three priorities emerged for our program moving forward. The first was to decode the mode of action behind this activity. The second was to decipher the functional effects of HMO structural diversity as there are ca. 200 unique HMOs present in human milk. Finally, we set our sights on discovering novel uses for HMOs as we believed this would uniquely position our team to achieve a major breakthrough in human health and wellness. Through a combination of fractionation techniques, chemical synthesis, and industrial partnerships, we have determined the identities of several HMOs with potent antimicrobial activity against the important neonate pathogen Group B Streptococcus (Group B Strep; GBS). In addition to a structure-activity relationship (SAR) study, we observed that HMOs are effective adjuvants for intracellular-targeting antibiotics against GBS. This included two antibiotics that GBS has evolved resistance to. At their half maximal inhibitory concentration (IC₅₀), heterogeneous HMOs reduced the minimum inhibitory concentration (MIC) of select antibiotics by up to 32-fold. Similarly, we observed that HMOs potentiate the activity of polymyxin B (Gram-negative-selective antibiotic) against GBS (Gram-positive species). Based on these collective discoveries, we hypothesized that HMOs function by increasing bacterial cell permeability, which would be a novel mode of action for these molecules. This hypothesis was validated as HMOs were found to increase membrane permeability by around 30% compared to an untreated control. The question that remains is how exactly HMOs interact with bacterial membranes to induce permeability changes (i.e., through promiscuous insertion into the bilayer, engagement of proteins involved in membrane synthesis, or HMO-capsular polysaccharide interactions). Our immediate efforts in this regard are to apply chemoproteomics to identify the molecular target(s) of HMOs. These investigations are enabled through manipulation of HMOs produced via total synthesis or enzymatic and whole-cell microbial biotransformation.

1-Amino-2'-fucosyllactose inhibits biofilm formation by Streptococcus agalactiae

2'-Fucosyllactose (2'-FL) is a ubiquitous oligosaccharide in human milk. Importantly, this carbohydrate promotes the growth of several strains of Bifidobacteria, a class of beneficial gut commensal, and inhibits epithelial binding of pathogens. In light of these protective effects, we elected to evaluate the potential of 2'-FL to serve as an antibacterial agent against Group B Streptococcus (GBS). While 2'-FL was devoid of any substantial antimicrobial or antibiofilm activity, conversion of 2'-FL to its reducing end β-amine provided a novel antibiofilm compound.

Sialylated Oligosaccharides and Glycoconjugates of Human Milk. The Impact on Infant and Newborn Protection, Development and Well-Being

Human milk not only has nutritional value, but also provides a wide range of biologically active molecules, which are adapted to meet the needs of newborns and infants. Mother’s milk is a source of sialylated oligosaccharides and glycans that are attached to proteins and lipids, whose concentrations and composition are unique. Sialylated human milk glycoconjugates and oligosaccharides enrich the newborn immature immune system and are crucial for their proper development and well-being. Some of the milk sialylated oligosaccharide structures can locally exert biologically active effects in the newborn’s and infant’s gut. Sialylated molecules of human milk can be recognized and bound by sialic acid-dependent pathogens and inhibit their adhesion to the epithelial cells of newborns and infants. A small amount of intact sialylated oligosaccharides can be absorbed from the intestine and remain in the newborn’s circulation in concentrations high enough to modulate the immunological system at the cellular level and facilitate proper brain development during infancy. Conclusion: The review summarizes the current state of knowledge on sialylated human milk oligosaccharides and glycoconjugates, discusses the significance of sialylated structures of human milk in newborn protection and development, and presents the advantages of human milk over infant formula.