Does the Human Gut Microbiota Contribute to the Etiology of Autism Spectrum Disorders?

Table 1 Microbiota differences determined in autism spectrum disorder subjects compared to control subjects

Study group	Methodology	Significantly higher in ASD	Significantly lower in ASD	References
13 ASD, 8 CON	Bacterial culture, feces	Clostridium and Ruminococcus spp.		Finegold et al. [16]
15 ASD, 8 CON	Quantitative PCR, feces	Clostridium clusters I and XI, Clostridium bolteae		Song et al. [17]
58 ASD, 12 SIB,10 CON	Fluorescent in situ hybridization, feces	Clostridium histolyticum group (Clostridium clusters I and II)		Parracho et al. [10]
33 ASD, 7 SIB, 8 CON	Pyrosequencing, feces	Severe ASD (11 subjects) versus CON: Phylum level: bacteroidetes and proteobacteria Genus level: Alkaliflexus, Desulfovibrio, Acetanaerobacterium, Parabacteroides, Bacteroides	Severe ASD (11 subjects) versus CON: Phylum level: firmicutes and actinobacteria Genus level: 14 genera, most significant and abundant: Weissella, Turicibacter, Clostridium, Anaerofilum, Pseudoramibacter, Ruminococcus, Streptococcus	Finegold et al. [8]
23 ASD, 22 SIB, 9 CON	Quantitative PCR, feces	Bacteroides fragilis in ASD subjects with GI symptoms only (9 of 23)	A. muciniphila (ASD and SIB); Bifidobacterium spp. (ASD only)	Wang et al. [11]
58 ASD, 39 CON	Bacterial culture, feces	Lactobacillus spp.; Bacillus spp.	Bifidobacterium spp., Enterococcus spp., Klebsiella oxytoca	Adams et al. [14]
15 ASD with GI symptoms, 7 CON with GI symptoms	Pyrosequencing and quantitative PCR, ileal and cecal biopsies	Cumulative level of firmicutes + proteobacteria; Sutterella spp.	bacteroidetes	Williams et al. [9, 18]

ASD Subjects with autism spectrum disorder, SIB non-autistic siblings, CON unrelated control subjects, GI gastrointestinal