The bacteria, Candida and Staphylococcus, live in biofilms on the surface of the retainer. A biofilm is a community of bacteria living together covered in a layer of slime. Biofilms are found anywhere a combination of moisture, nutrients, and a surface exists (that slimy layer on the sides of a pool or a hot tub are biofilms). Biofilms are usually so thin that they cannot be seen by the naked eye, but in certain cases they can become very thick and apparent. When this slimy film forms on the surface of the retainer it is very difficult to remove and it often has a high level of resistance to antimicrobials.
Finding these two potentially pathogenic microbes could indicate a need for the improvement of cleaning products for orthodontic retainers to eliminate the biofilms that house these toxic microbes. However, for now hygiene is the main method in reducing the transmission of these bugs. Mouthwashes and careful tooth brushing may help to keep the microbes off of the cheeks and tongue which in turn will keep it off of the retainer. It is also important to keep in mind that anyone who handles a retainer should be sure to wash their hands before and after handling.