Are there any possible connections between bacteria and autism?

None yet: There's a serious brain disease presenting primarily as behavior that follows strep infections -- PANDAS is the acronym. It's real and was readily accepted when a convincing case was made by a few physicians. By contrast, every claim for things that "cause" autism haven't stood up to scrutiny, and I believe their proponents are seeing faces in the clouds. Care for Junior, don't demand any "Why".