Biofilm can contain various biological entities. Which of the following is NOT typically included?

Biofilm is a complex aggregation of microorganisms that adhere to surfaces and each other, embedded in a self-produced matrix of extracellular polymeric substances. It commonly consists of various biological entities, mainly bacteria, protozoa, and fungi.

Bacteria are the primary constituents of biofilm and play significant roles in its formation, structure, and function. Protozoa can be present in biofilms, particularly in environments where they may interact with bacteria, providing a diverse ecosystem. Fungi can also be part of biofilms, especially in certain environments such as dental biofilms or in other moist conditions where they coexist with bacteria.

Viruses, on the other hand, are not typically included in biofilm. While they can influence microbial populations, they do not form biofilms in the same manner as the other microorganisms. Instead, they may infect bacteria or be involved in lytic cycles but do not adhere to surfaces and produce extracellular matrixes like bacteria, protozoa, or fungi do. Thus, viruses are not considered a component of biofilm in the traditional sense.