Re: Do all 'friendly' bacteria produce lactic acid? Any that don't?

Well, let’s start with your statement "the lactic acid they produce is a major cause of cavities".

Since the beneficial effects of good bacteria are primarily in the intestine, and your teeth are in your mouth, I'm not sure the fact that they produce lactic acid is really an issue.

My understanding of cavities is that they are caused by sugars, which are fermented by oral bacteria. When those sugars are fermented *in the mouth*, by bacteria essentially *stuck* to your teeth, the lactic acid is formed very close to the teeth, where is can cause tooth decay. So it's not lactic acid per se that causes the problem. It's much worse for your teeth to eat lots of sugar (which can stick to your teeth) and to not brush and floss regularly (to get rid of bacteria) that to worry about eating a little bit of lactic acid.

On to part two:

"I want to find out if there are non-pathogenic bacteria that don't produce lactic acid".

There are many, many non-pathogenic bacteria that do not produce lactic acid. Many organisms that spoil food do not produce lactic acid and will not make you sick.

But I think your implied question is: Are there probiotic producing bacteria that don't produce lactic acid? Using a strict definition: no. Using a more liberal definition (probiotics are anything that benefits human health): yes. There are some prescription-only preparations available in other countries that are used to treat infants with a protein- digestion deficiency.