The only way you can keep a "pure" influence would be to use the entire sample donated to you by the company (and even then, there will be local influence).

Bread doesn't pick up a ton of bacteria during it's fermentation period, it's the feeding cycle where it will. If you split the culture into many small ones, you're just guaranteeing all of them will be supplanted the moment they're fed.

Can't you sterilize what you're feeding it? I don't get it.

Sterilize it how? There's inert yeast and bacteria on your flour at all times. That's what allows you to create a starter from scratch. What do you want to do, bleach raw flour every time you're about to drop it in your starter?

I'm sure if you were in a lab environment and absolutely needed to, there are options to do so. But not for most home bakers.