"Our review includes two randomized controlled trials, which showed improvement of ASD [autism spectrum disorder] behaviors, and three open trials, all which exhibited a trend of improvement."
So said the findings reported by Jun Liu and colleagues  and the results of their "updated systematic review" on the topic of probiotic 'therapy' in the context of behaviour and gastrointestinal (GI) functioning in autism.
The current scientific outlook for probiotic use in the context of autism looked to be pretty good on the basis of the Liu findings. They corroborate quite a few individual study results that have been fodder for this blog (see here and see here) and fit in well with an emerging pattern of research suggesting that the trillions of wee beasties that inhabit the gastrointestinal (GI) tract might be doing a lot more than just helping us digest food (see here and see here).
What else is required? Well Liu et al talk about more "rigorous trials" to answer questions like who on the autism spectrum might be a best responder to this type of intervention and what bacterial species might be most important. I'd also like to see a little more research on the hows-and-whys of such intervention (see here for example) and whether probiotics are as harmless as many have made them out to be.
 Liu J. et al. Probiotic Therapy for Treating Behavioral and Gastrointestinal Symptoms in Autism Spectrum Disorder: A Systematic Review of Clinical Trials. Curr Med Sci. 2019 Apr;39(2):173-184.