Specific species of bacteria have indeed been found that can catabolize specific types of plastics.
In some niches they will definitely evolve to decompose plastics.
Since all life forms on earth rely heavily on water as solvent (being present ideally all the time), those 'invasive' bacteria won't have that much of an effect on humanity's habits IMHO, since regularly removing the water easily keeps their impact low.
Fungi might play an important role in decomposition of plastics as well, since they have advantages over bacteria that may be relevant for decomposition of plastics in the same way in which they are for decomposing wood.
(Which is difficult for bacteria)
