We've been interacting with microbes for a long time too, not just in terms of immunity and disease but in deliberate acts. So how did we go about doing microbiology before we discovered microbes? When I say 'microbiology' I'm being greedy and gathering in anything to do with microbes under a big net. Lots of the more general, practical applications of microbiology don't necessarily require much knowledge of microbes at all!
Let's start with food. Bread is one of the oldest types of food, and an excellent example of microbes being used for good; yeast (Saccharomyces cerevisiae. Didn't have to look up the spelling of that, I hope you're impressed) pumps out CO2 making the bread rise. Shut off the oxygen and the yeast pumps out ethanol (see this previous post for more), allowing for production of beer and other alcohols.
Food preservation is microbiology too; food going off is all done by microbes, so to preserve food we need to do something to stop them growing. Curing meats by salting them is a classic one, leading to conditions too dry for bacteria and fungi to grow. Sugar does a similar thing; preserving using sugar (things like jams and other preserves/conserves) seems counter-productive as bugs love sugar, but in large amounts it has drying properties the same as salt. Pickling in alcohol works well too because the ethanol is antimicrobial (that's why I use it all day in the lab to keep things sterile!).
It's not just chemicals and compounds you can use to preserve food though; adding friendly bacteria to food can stop other less friendly bacteria growing. I love meats like salami and chorizo, but did you know they're raw? They're preserved by lactic acid bacteria which (as the name suggests) produce lots of acid, making conditions too hostile for other microbes to grow. Cheese and yoghurt, too, are full of microbes (at least in the preparation stages, some are pasteurised before selling the stuff) added to produce acids and fend off the bacteria we don't want. That's why cheese and yoghurt are gloopier than milk; the acid changes the shape of proteins like casein, thus changing the consistency of the food.
It's not just food and drink though, or even just friendly bacteria; we've been using microbes aggressively for centuries. Archers used to stab their arrows into the ground, coating the heads with soil bacteria leading to increased risk of infection from any wounds. During the siege of Kaffa the Mongols besieging the town were hit by the plague (Yersinia pestis), so instead of letting it go to waste they shared it with the townspeople by catapulting plague corpses over the walls. Probably a poor move as escapees from the siege went on to spread it to the whole of europe, more commonly referred to as the Black Death pandemic. Smallpox (ooh look a virus, I don't talk about them much) gave the Spanish a massive accidental advantage in their conquest(s) of South America, and then again in North America when it was spread more deliberately by the British via smallpox blankets (I know this happened after the discovery of microorganisms but I'm putting it in anyway, it's my blog!).
This is not even close to an exhaustive list! They all show huge, world-changing uses (intentional and otherwise) of microbes and microbiology years, centuries and millenia before the discovery of 'animalcules' by Anton van Leeuwenhoek in the late 1600s.