Hollie Statzer

 Introduction. Autism spectrum disorder (ASD) is a neurodevelopmental disorder with a possible relationship with GI dysregulation.^1,2 A novel Clostridium species, C. bolteae, was determined to be present at significantly higher levels in children with ASD.^3,4 Short chain fatty acids (SCFAs) possess the ability to alter cognitive function. Butyrate and propionic acid (PPA) are SCFA byproducts of anaerobic fermentation linked to neurodevelopmental disorders.^5,6 SCFAs can contribute to increased catecholamine levels, which may explain the increased sympathetic tone and anxious behaviors of ASD.^5,7-9 Understanding how C. bolteae disrupts microbiome SCFAs may be useful for developing of ASD treatments and diagnostic tests. Methods. Fecal samples were taken from age-matched children with and without ASD. Fecal weight and product concentration were used to calculate fermentation products.⁶ Strains of C. clostridioforme and C. bolteae were isolated from patients in two hospitals over a two year period.¹⁰ PCR was performed on the isolates, and genome sequencing was performed to identify antibiotic-resistance genes. Another study utilized gas chromatography to assess lipids extracted from brain tissue collected from rats with propionic acid (PPA)-induced autistic features.¹¹ Rats were inoculated with isolated C. bolteae capsular polysaccharide and serum was analyzed for antibodies.¹² Results. SCFAs were present at higher levels in children with ASD compared with controls (136.6 ± 8.7 vs. 111.1 ± 6.6 mmol/kg, p=.012).⁶ Ammonia (42.7 ± 3.3 vs.32.3 ± 1.9 mmol/kg, p=.007) and butyric acid (24.5 ± 1.8 vs. 19.5 ± 1.5, p=.025) levels were higher in these children as well.⁶ Comparisons showed C. bolteae utilizes different flagellar systems and butyrate pathways than C. clostridioforme.¹⁰ Both species possess beta-lactam resistance, but resistance genes unique to C. bolteae include tetracycline protein (TetO) and D-alanyl-D-alanine carboxypeptidase (VanY_G).¹⁰ The concentration of butyric acid was significantly higher in PPA-treated rats than controls (0.894 ± 0.086 vs. 0.540 ± 0.126 mmol/gm brain tissue, p<.001).¹¹ Pearson correlation revealed a significant correlation between the PPA-treated rats with ASD features and butyric acid concentration (R=0.845, p<.001). Isolation of C. bolteae showed that capsular polysaccharides were comprised of mannose and rhamnose units [→3)-α-D-Manp-(1→4)-β-d-Rhap-(1→].¹² Serum IgG antibodies to the capsular polysaccharide were present at 1:1000 dilution.¹² Conclusions. One possible mechanism by which the intestinal microbiome relates to ASD is through anaerobes such as C. bolteae. Butyric acid and other SCFA byproducts of C. bolteae may possess potential for the development of autism diagnostic tests. Proteins and capsular polysaccharides unique to C. bolteae provide potential targets for therapeutic treatments.

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