# Microbes in Health and Disease: Human Gut Microbiota
## 4 Associations with Human Diseases
For example, in a Chinese study recruiting 34 infants with food allergy (17 IgE-mediated and 17 non-IgE-mediated) and 45 healthy controls, the food allergy was associated with fewer phyla _Bacteroidetes_, _Proteobacteria_, and _Actinobacteria_ and fewer genera _Enterococcus_ and _Staphylococcus_ but with high phylum _Firmicutes_ and high family _Clostridiaceae_ 1; particularly, IgE-mediated allergy was associated with increased _Clostridium sensu stricto_ and _Anaerobacter_ and decreased _Bacteroides_ and _Clostridium_ XVIII, suggesting the relevance of dysbiosis of the gut microbiota in food allergy [119]. In a Canadian study recruiting 166 infants in the first year of life, low fecal microbiota richness at 3 months and a high Enterobacteriaceae/Bacteroidaceae ratio in early infancy were associated with subsequent food sensitization [120]. In a USA study recruiting 141 children aged 3-16 months, children with egg allergy (\(n=66\)) harbored abundant genera from the _Lachmospiraceae_ and _Streptococcus_ families, while controls without egg allergy (\(n=75\)) harbored abundant _Leuconostocaceae_[117]. An animal study previously showed that Clostridia-containing microbiota protected against food allergen sensitization [116], and the anaerob _Anaerostipes caccae_ from the feces of a healthy infant was found to prevent food allergy in mice [121]. The association of non-food allergies with the gut microbiota was also observed [122]. For example, in a large birth-cohort study in the Netherlands, an increased risk of developing eczema among infants was found to be associated with increasing numbers of gut _Escherichia coli_, and the presence of _Clostridium difficile_ was associated with an increased risk of developing eczema, recurrent wheezing, and allergic sensitization [122]. In a longitudinal study including 25 infants at high risk for asthma (HR) and 29 healthy controls, HR infants were randomized to daily oral _Lactobacillus rhamn_ GG (HRLGG) or placebo (HRP) for 6 months, and delayed gut microbiota diversification over the first year of life was observed in HRP subjects; however, the rate of bacterial gut microbiota diversification in HRLGG subjects was comparable to that in healthy controls, suggesting that the associations of childhood atopy and asthma with perturbation and delayed development of early-life gut microbiota can be temporally modified by _Lactobacillus_ supplementation [123]. In a study including 25 participants with dementia due to Alzheimer's disease (AD) and 25 control participants, the AD group presented decreased gut microbiota diversity and Firmicutes but increased Bacteroidetes as well as decreased _Bifidobacterium_, and there was a significant association of the cerebrospinal fluid (CSF) biomarker YKL-40 with the abundances of _Bacteroides_, _Turicbacter_, and the genus SMB53 (family _Clostridiaceae_) [124]. A systematic review identified differences in the gut microbiota of 53 microbial families and 98 genera between subjects with Parkinson's disease (PD) and healthy controls. The genera with increasing trends in PD reported in two studies included _Bifidobacterium_, _Alistipes_, _Christensenella_, _Enterococcus_, _Oscillospira_, _Bilophila_, _Desulfovibrio_, _Escherichia/Shigella_, and _Akkernansia_, and the genera with decreasing trends in PD reported in two studies included _Prevotella_, _Blutia_, _Faecalibacterium_, _Fusicatenibacter_, and _Haemophilus_[125].