Table presents taxa with increased relative abundance and ta
Table 3 presents 14 taxa with increased relative abundance and 3 taxa with decreased relative abundance with Cesarean birth history. Cesarean-delivered adults had nominally reduced abundance of Coprobacillus and Holdemania (phylum Firmicutes) and of Neisseria (Proteobacteria), as well as nominally increased abundance of five genera in the Lachnospiraceae, Peptococcaceae, and Ruminococcaceae fccp of Clostridia (Firmicutes), Dysgonomonas (Bacteroidetes, Bacteroidales) and Salmonella and Haemophilus (Proteobacteria, Enterobacteriaceae). Table 3 also shows the 22 taxa (14 Proteobacteria, 3 Actinobacteria, 3 Bacteroidetes, and 2 Firmicutes), all increased, with appendectomy history. These are nominally significant associations, none of which survived adjustment for multiple comparisons. Mean relative abundances for all 1949 taxa and Wald P-value comparisons are provided in Supplemental Table 2.
Discussion This analysis was primarily motivated by the observation that the composition of the microbiome of neonates differed significantly between those born vaginally and those born by cesarean section (Arrieta et al., 2014; Dominguez-Bello et al., 2010). With vaginal delivery, the neonatal microbiome resembled the vaginal microbiome, with high relative abundance of Prevotella and especially Lactobacillus taxa. In contrast, cesarean-delivered neonates had a diverse array of taxa resembling the skin microbial community, including Staphylococcus, Streptococcus, Propionibacterineae, Haemophilus, and Acinetobacter (Dominguez-Bello et al., 2010). Cesarean-delivered neonates and infants typically have a paucity of Bifidobacterium and Bacteroides species (Arrieta et al., 2014). In the current analysis, we observed that the fecal microbiome composition differed in adults who reported that they had been delivered by cesarean section. This suggests that a difference by route of delivery may persist into adulthood. Of the taxa noted to be increased in cesarean-delivered neonates and infants (Arrieta et al., 2014; Penders et al., 2006; Dominguez-Bello et al., 2010), only Haemophilus and certain Clostridia genera had elevated abundance in the fecal microbiome of cesarean-delivered adults (Table 3). In the placenta, microbiome composition (beta diversity) was reported to generally resemble the healthy oral microbiome. Placenta microbial composition differed for two types of women — those who reported a first-trimester urinary tract infection, with enrichment of several genera including Streptococcus and Acinetobacter; and those who had a pre-term delivery, with enrichment of Burkholderia and other genera (Aagaard et al., 2014). No overlap was observed between these taxa and the taxa that we found to differ, with nominal statistical significance, in the fecal microbiome of adults who had been born by cesarean section or who reported removal of their appendix (Table 3). The placenta microbiome was not found to differ between cesarean and vaginal birth (Aagaard et al., 2014). Our study had several strengths, including relatively large size; high quality, unbiased profiles of the microbiome; restriction to individual adults; careful exclusion of recent antibiotic use and medical conditions that might have altered the microbiota; state-of-the-art statistical methods; and comparison of two conditions postulated to alter the gut microbiota. Although widely dispersed across the USA, the participants were not representative of the American adult population, being overwhelmingly non-Hispanic Caucasian (93%) and non-smokers (96%). Nonetheless, the prevalence of cesarean birth in our population, which was born on average in 1967, was 8.8%, comparable to the estimated cesarean rates of 5.5% and 10.4% for births throughout the USA in 1970 and 1975, respectively (Anon., 1995). The prevalence of appendectomy in our study, 14%, was similar to the 11%–14% prevalence reported by Dutch and British general population controls (Russel et al., 1997; Gent et al., 1994).