Is it true that they put s type of bacteria in ice cream to make it smoother?

Sombody already siad this, but they need bacteria to turn the ミルク into cream. As far as I know, bacteria does not make it smoother.

I just wanted to add that if あなた are talking about the soft serve icecream at places like Macdonalds, they pig fat and flavoring rather than real milk, so it is really smooth.

yes

Of course. Bacteria is needed to make cheese, yogurt, ice cream, ミルク and dairy. Without it, it is not dairy. But it is good bacteria anyway. Like Yakult and Vitagen.

yes, it's in yogurt 2 but it's not bad bacteria

Yes, its in all Dairy products to kill germs from the cow ect. Your science teacher told あなた so I'm gessing he/she is right!