In alternative embodiments, provided are pharmaceutical compositions and methods for treating, ameliorating, reversing and/or preventing (acting as a prophylaxis) autism, e.g., regressive autism. In alternative embodiments, these pharmaceutical compositions and methods are dosaged and administered to children in need thereof. In alternative embodiments, pharmaceutical compositions and methods are dosaged, formulated and dosaged as solid, liquid or aerosol preparations or formulations. In alternative embodiments, pharmaceutical compositions comprise rifaximin as the sole antibiotic, or rixafimin and other antimicrobial or antibiotic agent, for example, vancomycin, metronidazole, tinidazole or a combination thereof.
