Combined abdominal and transcranial photobiomodulation is associated with fecal microbiome restructuring: a systems...

Photobiomodulation (PBM) has been proposed as a non-invasive strategy capable of modulating mitochondrial, inflammatory, vascular, and gut-brain axis-related pathways. However, its potential effects on fecal microbiome ecology in neurobehavioral conditions remain poorly characterized. This case report describes paired fecal microbiome findings before and after a 90-day combined abdominal and transcranial PBM protocol in a 6-year-old female with autism spectrum disorder and chronic constipation. PBM was delivered daily using a 1064-nm near-infrared LED device with 54 mW/cm² irradiance, applied for 10 min over the right prefrontal cortex and for 10 min over the infraumbilical and right lower abdomen. Fecal samples collected before and after the intervention were analyzed by 16 S rRNA amplicon sequencing. The baseline sample showed limited taxonomic resolution, with 93.14% assigned to "Other/unclassified," whereas the post-intervention sample showed a more taxonomically resolved microbial profile, including Firmicutes (53.37%), Bacteroidetes (29.66%), Actinobacteria (7.97%), Verrucomicrobia (4.21%), Euryarchaeota (2.89%), Proteobacteria (1.14%), and a markedly reduced unclassified fraction (0.03%) at the phylum level. At the genus level, the post-intervention profile showed detection or increased representation of taxa commonly discussed in relation to gut microbial ecology, mucosal biology, and short-chain fatty acid metabolism, including Faecalibacterium (7.03%), Bifidobacterium (4.25%), Bacteroides (18.82%), Alistipes (5.38%), preserved Akkermansia (3.92%-4.21%), and low-abundance Roseburia. Taxa with context-dependent or uncertain significance, including Sarcina, Collinsella, Parabacteroides, and residual unclassified genera, were also observed and are reported transparently. Caregiver behavioral observations included improved bowel regularity, reduced abdominal distension, more stable mood, reduced irritability and impulsivity, improved communication, and greater social tolerance. The intervention was well tolerated with no reported adverse effects. As a single-patient pre-post case report without sham control, repeated baseline sampling, or functional metagenomic confirmation, these findings cannot establish causality. Nevertheless, they provide a biologically plausible systems-level observation linking combined abdominal and transcranial PBM with a shift in fecal microbiome structure and gastrointestinal-behavioral regulation, supporting future controlled studies integrating longitudinal microbiome profiling, metabolomics, inflammatory biomarkers, autonomic measures, and validated behavioral outcomes.