Table 1.

Effect of different microbes in autistic patients.

Name of microbes	Microbial level in autistic patients	Effect in autistic patients	References
Proteobacteria	Increases	It caused host inflammation and reduction in levels of GSH. It also led to the production of LPS which is the major cause of immune dysregulation in autism.	36,37
Bacteroides	Increases	It produces short chain fatty acids and their metabolites especially propionic acid which may influence autism behavior by gut brain axis.	51
Clostridium	Increases	It produces endotoxins and propionate that may be associated with severity of ASD symptoms.	40, 41, 42, 43
Faecalibacterium prausnitzii	Increases	It produces anti-inflammatory butyrate which is regarded as commensal or even beneficial in children with autism.	47
Candida albicans	Increases	It results in absorption of carbohydrates and releases ammonia which leads to excess of GABA production that can lead to the appearance of autistic behavior.	49
Bifidobacterium	Decreases	Bifidobacterium synthesize GABA, as its level decreases in autism so children with autism have low levels of GABA.	52
Blautia	Decreases	This bacterium has role in synthesis of Tryptophan and bile acid that acts as a precursor of Serotonin. Hence, its lower levels leads to less serotonin in brain and can be correlated to autistic behavior.	53
Prevotella	Decreases	Involved in metabolism of saccharides due to which autistic patients are thought to have impaired Carbohydrate metabolism.	54

GSH- Glutathione; LPS- Lipopolysaccharide; ASD- Autism Spectrum Disorder; GABA- Gamma aminobutyric acid.