title: Having older siblings is associated with gut microbiota development during early childhood.
abstract: BACKGROUND
  Evidence suggests that early life infections, presence of older siblings and furred pets in the household affect the risk of developing allergic diseases through altered microbial exposure. Recently, low gut microbial diversity during infancy has also been linked with later development of allergies. We investigated whether presence of older siblings, furred pets and early life infections affected gut microbial communities at 9 and 18 months of age and whether these differences were associated with the cumulative prevalence of atopic symptoms of eczema and asthmatic bronchitis at 3 years of age. Bacterial compositions and diversity indices were determined in fecal samples collected from 114 infants in the SKOT I cohort at age 9 and 18 months by 16S rRNA gene sequencing. These were compared to the presence of older siblings, furred pets and early life infections and the cumulative prevalence of diagnosed asthmatic bronchitis and self-reported eczema at 3 years of age.
  
  
  RESULTS
  The number of older siblings correlated positively with bacterial diversity (p = 0.030), diversity of the phyla Firmicutes (p = 0.013) and Bacteroidetes (p = 0.004) and bacterial richness (p = 0.006) at 18 months. Further, having older siblings was associated with increased relative abundance of several bacterial taxa at both 9 and 18 months of age. Compared to the effect of having siblings, presence of household furred pets and early life infections had less pronounced effects on the gut microbiota. Gut microbiota characteristics were not significantly associated with cumulative occurrence of eczema and asthmatic bronchitis during the first 3 years of life.
  
  
  CONCLUSIONS
  Presence of older siblings is associated with increased gut microbial diversity and richness during early childhood, which could contribute to the substantiation of the hygiene hypothesis. However, no associations were found between gut microbiota and atopic symptoms of eczema and asthmatic bronchitis during early childhood and thus further studies are required to elucidate whether sibling-associated gut microbial changes influence development of allergies later in childhood.
authors.affiliation: Division of Diet, Disease Prevention and Toxicology, National Food Institute, Technical University of Denmark, Mørkhøj Bygade 19, DK-2860, Søborg, Denmark. mfrla@food.dtu.dk.
authors.forename: Martin Frederik
authors.initials: MF
authors.lastname: Laursen
authors.affiliation: H.C. Andersen Children's Hospital, Odense University Hospital, Sdr. Boulevard 29, DK-5000, Odense C, Denmark. gitte.zachariassen@rsyd.dk.
authors.forename: Gitte
authors.initials: G
authors.lastname: Zachariassen
authors.affiliation: Division of Diet, Disease Prevention and Toxicology, National Food Institute, Technical University of Denmark, Mørkhøj Bygade 19, DK-2860, Søborg, Denmark. mbah@food.dtu.dk.
authors.forename: Martin Iain
authors.initials: MI
authors.lastname: Bahl
authors.affiliation: Division of Diet, Disease Prevention and Toxicology, National Food Institute, Technical University of Denmark, Mørkhøj Bygade 19, DK-2860, Søborg, Denmark. bergstrom@nexs.ku.dk.|Department of Nutrition, Exercise and Sports, University of Copenhagen, Rolighedsvej 30, DK-1958, Frederiksberg C, Denmark. bergstrom@nexs.ku.dk.
authors.forename: Anders
authors.initials: A
authors.lastname: Bergström
authors.affiliation: H.C. Andersen Children's Hospital, Odense University Hospital, Sdr. Boulevard 29, DK-5000, Odense C, Denmark. Arne.Hoest@rsyd.dk.
authors.forename: Arne
authors.initials: A
authors.lastname: Høst
authors.affiliation: Department of Nutrition, Exercise and Sports, University of Copenhagen, Rolighedsvej 30, DK-1958, Frederiksberg C, Denmark. kfm@nexs.ku.dk.
authors.forename: Kim F
authors.initials: KF
authors.lastname: Michaelsen
authors.affiliation: Division of Diet, Disease Prevention and Toxicology, National Food Institute, Technical University of Denmark, Mørkhøj Bygade 19, DK-2860, Søborg, Denmark.
authors.forename: Tine Rask
authors.initials: TR
authors.lastname: Licht
mesh_terms: D001249:Asthma / Q000453:epidemiology*; D001419:Bacteria / Q000145:classification* / Q000235:genetics*; D002675:Child, Preschool; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D004485:Eczema / Q000453:epidemiology*; D005243:Feces / Q000382:microbiology; D000069196:Gastrointestinal Microbiome; D006801:Humans; D007223:Infant; D064307:Microbiota; D008969:Molecular Sequence Data; D010802:Phylogeny; D015995:Prevalence; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA; D035781:Siblings
chemical_list: D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D012336:RNA, Ribosomal, 16S