This is a semi-valid concern. It would take a relatively small amount of an organism to contaminate something, and unless you're regularly cleaning everything made of those types of plastics you could have some real issues.
We fight mold and termites now in our living spaces, imagine if you had a plastic-eating organism and a little bit took up residence in a hotel, an office, your car, a bus or train, your house.
Even if it was relatively slow at breaking down it could cause considerable cosmetic damage. A little gets on your laptop display. You leave it at home and go on vacation for a week, you come back and some light etching has occurred over streaks of your monitor and the screen is now fogged and needs replaced, you wipe the exterior down as best as you can before replacing the screen and are pretty sure you got it all. Your screen gets replaced, your laptop works great again until a month later you pick it up and your spacebar falls off, the plastic switch entirely degraded, you open up the laptop only to find most of the internal plastic is structurally compromised, you unknowingly transferred some of the organism inside when you replaced your screen.
Here in Indiana, sometimes in the spring and summer, there's this fungus called 'lawn rust' that has orange spores that resemble rust and get on your lawn and will even get on vehicles (which will just wash off) but imagine something getting in the wild and landing on your car with a largely plastic body... go a week or a month without washing your car and you might get home from the car wash one day and notice your bumpers are pitted, oh darn the future plastic eating bacteria/fungi strikes again.
Even if only kept this stuff in industrial facilities, unless you go NASA level clean-room when leaving the facility it'd be damn easy for some to hitch a ride on someone headed home from work and, well, "life will find a way".