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BackgroundStaphylococcus aureusis a leading cause of healthcare- and community-associated infections and can be difficult to treat due to antimicrobial resistance. About 30% of individuals carryS. aureusasymptomatically in their nares, a risk factor for later infection, and interactions with other species in the nasal microbiome likely modulate its carriage. It is thus important to identify ecological or functional genetic elements within the maternal or infant nasal microbiomes that influenceS. aureusacquisition and retention in early life.ResultsWe recruited 36 mother-infant pairs and profiled a subset of monthly longitudinal nasal samples from the first year after birth using shotgun metagenomic sequencing. The infant nasal microbiome is highly variable, particularly within the first 2 months. It is weakly influenced by maternal nasal microbiome composition, but primarily shaped by developmental and external factors, such as daycare. Infants display distinctive patterns ofS. aureuscarriage, positively associated withAcinetobacterspecies,Streptococcus parasanguinis,Streptococcus salivarius, andVeillonellaspecies and inversely associated with maternalDolosigranulum pigrum. Furthermore, we identify a gene family, likely acting as a taxonomic marker for an unclassified species, that is significantly anti-correlated withS. aureusin infants and mothers. In gene content-based strain profiling, infantS. aureusstrains are more similar to maternal strains.ConclusionsThis improved understanding ofS. aureuscolonization is an important first step toward the development of novel, ecological therapies for controllingS. aureuscarriage.

Additional file 10: Review history.

Objectives’To determine the patterns ofS. aureuscarriage in the first year of life, its determinants and dynamics of transmission between mothers and infants.MethodsProspective longitudinal cohort study ofS. aureuscarriage among mothers and their infants. Monthly screenings from pregnancy/birth through the first year of the infant’s life. Medical and lifestyle data was collected. InfantS. aureuscarriage was detected by rectal and nasal swabs and maternal carriage by nasal swabs. Multivariate analysis and an NLMixed model were used to determine predictors of carriage andS. aureuspersistence.Results130S. aureuscarrier women and their 132 infants were included in the study. 93% of the infants acquiredS. aureussometime during the first year of life, 64% of them acquired the maternal strain, mostly (66%) during the first month of life. 70 women (52.50%) and 17 infants (14%) carriedS. aureuspersistently. Early acquisition ofS. aureuscarriage was associated with longer duration of initial carriage and was the most significant predictor ofS. aureuspersistence, while day-care center attendance was negatively associated with persistent carriage.ConclusionsEarly acquisition ofS. aureus, mostly from the mother, is an important determinant of carriage persistence in infancy.

S. aureus and S. pneumoniae are both common pathogens that are also carried by a large proportion of healthy individuals in the nasal and nasopharyngeal spaces. A negative association between carriage of S. aureus and S. pneumoniae has been reported in children in various epidemiologic studies from different geographical regions. Most studies found that the negative association between S. pneumoniae and S. aureus was significant only for carriage of vaccine-type S. pneumoniae strains. In this review, we summarize the various suggested mechanisms of this suggested bacterial interference, and the clinical implications reported following PCV introduction to date in various geographical regions.

Staphylococcus aureus is a pathogen that causes significant morbidity and mortality. Nasal carriage is a major source of transmission and of endogenous infection. Persistent carriage is detected in ∼30% of healthy individuals. While Th17 cells have been shown to play a role in S. aureus infection and clearance, the immune response to carriage is not well understood. Here, we evaluate the Th17 response and its potential inhibitors during S. aureus carriage. We recruited 25 volunteers, of whom 11 were persistent carriers. Volunteers' peripheral blood mononuclear cells (PBMCs) were stimulated with either their endogenous strain (a strain isolated from that carrier) or exogenous ones (strains not carried by that volunteer). Changes in Th17 cell frequency and numbers, interleukin-17 (IL-17) mRNA expression, and IL-17 protein abundance were measured by fluorescence-activated cell sorting, real-time PCR, and enzyme-linked immunosorbent assay. Similarly, responses of IL-17 suppressors (regulatory T cells [FOXP3], IL-10, IL-27, and IL-19) were measured. Th17 and IL-17 levels in response to stimulation with endogenous strains were significantly lower than those in response to stimulation with exogenous ones. Of the suppressive cytokines tested, only IL-19 exhibited a stronger response to endogenous than to exogenous strains. Addition of recombinant IL-19 to exogenous-strain-stimulated PBMCs caused decreased IL-17 expression, whereas addition of IL-19 antibodies to endogenous-strain-stimulated cells resulted in an increased IL-17 response. Together, our results suggest that S. aureus carriage induced a tolerogenic response to a carried strain that could be reproduced through the addition of recombinant IL-19 or prevented by the addition of IL-19 antibodies. This differential immune response may play a role in the determination of S. aureus carriage patterns.