Imbalances in the intestinal flora as a result of early antibiotic use, for example, have also been implicated in the development of autism. Probiotics have been shown to aid in the treatment of autistic symptoms by promoting the growth of beneficial bacteria and inhibiting the growth of harmful bacteria. Researchers have identified an overgrowth of certain strains of Clostridia that produce propionic acid in the guts of autistic children. Propionic acid is a neurotoxin that crosses the blood-brain barrier and could disrupt normal brain development in early childhood (Parracho, Gibson, Knott, Bosscher, Kleerebezem, & McCartney, 2010).