Wood-eating bacteria already exist and we use wood as a material for many things. It's not like such bacteria just spread from breath, like covid-viruses...
Look up shipworm, which historically took out many ships. Plenty of stuff eats wood quickly enough to cause issues. We have just evolved countermeasures. And trees are the product of a billion years of anti-predator evolution. Plastic is different than wood. It is homogenous and dead. Something like a plastic-eating bacteria might move through it exponentially.
There are plenty of old wooden houses still standing (even ones which predate modern plastic based paints), people still make boats out of wood too. I suspect similar things will happen with plastic, we'll learn to build and protect plastic in the way that we used to do with wood, and probably more stuff will be built out of stone.