Hard cheese probably won't let you recover any bacteria - the water activity [amt of available water, a good indicator of how friendly to micro growth, typically determined by moisture content + salt level] on them is fairly low.
New opportunistic mold spores have a good time, but the bacteria which created the acidic conditions for the protein coagulation as mostly MIA or super hard to get to grow again.
It's easy to get bacteria from soft cheeses. They don't add any chemical to kill the bacteria, they don't have to. And, they're not going to pasteurize the cheese...heating it up to 170 would have some predictable textural consequences you can try out in your own microwave...
HOWEVER, although I did make cheese - in fact I also made Brie [more on this in a moment] - there were some difficulties.
1) biggest issue, all my cheese had a very estery off taste. Esters are the kind of things you smell on fruit when it's very ripe. Think of a banana + a pear + an overripe cantaloupe + a mushy apricot + a bunch of sickly sweet sweaty sock smells...I did 8 or so cheese making sessions and they all ended up like this
2) I don't have a good "control", my reclaimed culture did the above smelling thing...but I made 3 thermophillic cheeses as well from store-bought yoghurt. All these cheeses were made from the same local fresh-from-that-day goat milk as my recaptured culture...so what's the problem isolating these results and comparing them to the recapture?? Mostly because I'm an idiot and didn't plan ahead. The first I made a crumbled into salad while my first mesophilic cheeses were still finishing. So, I didn't have any to taste later because i used it up right away. I don't THINK it had any estery taste. The second used a blend of both cultures...yup, weird taste. The third--I was getting my act together here and not using the reclaimed mesophillic culture--was supposed to be Mozz and it melted in the pot and became more of a tragedy than a mess.
3) So, was it the goat milk [or the bacteria therein] or my culture? I wanted to purchase a pack of store-bought culture and see if it got the funky taste but the goats are dried up...maybe next year. IF store-bought culture results in weird tasting cheese, then I'll have to find ways to eliminate it--my main method would be to pasteurize the milk first on the stove-top and then culture it. But DANG it was easy to make cheese - plop in spoonful of culture, set, stir rennet, cut & drain - press/age/wrap as needed.
4) Okay - that brie. So I inoculated a cut up chunk of brie into the cheese after blending. That was going okay in the fridge for aging but not great. So I sliced off a few little bits more of the rind from a finished cheese and put them on my new cheeses rind. Wait 2 weeks. = Brie. But that Brie funk + my fruity ester funk. Wow, very hard to eat. I DID put some on english muffins [pre-toasted] and baked them until the brie was bubbly and just browning. I desperately wanted to volatilize those esters. It mostly worked. The cheese was practically delicious.
In sum, my wife started complaining about the work to milk the goats, make the cheese...and get what we got...and after I'd had my chance to experiment and learn to make soft, hard, stretched, and rinded cheeses took its course...I had to agree
I'll get some bulk cow's milk from a local place this winter and try again - at least a 1 gallon batch with reclaimed bacteria and see if the esters remain.