A biofilm is a group of microbes (most often bacteria, sometimes mixed with fungi) that clump together and surround themselves with a sticky, self-made coating. This coating is sometimes described as a “slime” or matrix, and it helps the organisms attach, communicate, and survive. The matrix is made from materials the microbes produce, including sugars, proteins, and DNA.
Biofilms are commonly linked to surfaces, like teeth (dental plaque), tissues, and medical devices. At the same time, they can also form as microbial aggregates within mucus layers on mucosal surfaces, which is one reason they come up in chronic or recurrent infection patterns.
What makes biofilms clinically relevant is how differently they can behave compared to individual, free-floating microbes. In a biofilm state, the matrix can limit exposure to antimicrobials and help organisms tolerate immune defenses. Some biofilm infections are also described as resisting phagocytosis, meaning immune cells may have a harder time clearing them once the community is established.