I was once told by a chemist that bacteria breaking down plastic is not an unthinkable thing. He said it's chemically quite similar to something existing (fat?)

I was once told by a chemist that bacteria breaking down plastic is not an unthinkable thing. He said it's chemically quite similar to something existing (fat?), so once bacteria stop ignoring plastic due to details in their chemical fingerprint, they can break it down. They would be able to do so already if not for said details. Hope I remember correctly.