Ahh yes, biofilms. These protein matrixes are like scum build-up in your bathtub for example. In the body, your immune-cells keep them under control to some extent by sloughing off cells underneath them. On other surfaces like mucus membranes, we have a slime layer--mucus which gives us protection. In the mouth, there are enzymes in the saliva which help control it, but some people have more trouble than others.
Some bacteria, will automatically morph into a biofilm as a means of survival, when there is no nutrients around to support them. Sometime other microbes will feed off these biofilms.
This is all part of natural events happing inside living things. Shroom