I wonder if the use of some antibiotics in infants kills beneficial gut bacteria that is normally present.
YES!
But it doesn’t cause ASD. At least not alone.
https://www.sciencedaily.com/releases/2022/02/220218080246.htm
For newborns that had been prescribed antibiotics, there was found to be a significant decrease in the levels of different Bifidobacterium species compared with babies who had no antibiotic treatment.
These microbes aids in the digestion of human breast milk and promotes gut health, while also supporting the immune defence against infection.
The team also found an increase in potentially disease-causing bacteria and in the number and abundance of genes related to antimicrobial resistance in the group that received antibiotics.