Which of the following is an example of a biofilm?

• A. A virus infecting a host cell
• B. Dental plaque on teeth
• C. A pure colony on an agar plate
• D. A single E. coli cell in liquid culture

Answer: (B)

Verified step by step guidance

1. Understand the definition of a biofilm: it is a complex community of microorganisms that adhere to a surface and are embedded within a self-produced matrix of extracellular polymeric substances (EPS).
2. Analyze each option to see if it fits the biofilm criteria: a virus infecting a host cell is a single pathogen-host interaction, not a community of microbes.
3. Consider a pure colony on an agar plate: although it is a group of microbes, it is a colony grown on a solid medium, not necessarily embedded in a matrix on a surface like a biofilm.
4. Look at a single E. coli cell in liquid culture: this is an individual cell in suspension, not a community attached to a surface.
5. Recognize that dental plaque on teeth is a classic example of a biofilm because it consists of multiple microbial species attached to the tooth surface within a matrix, fulfilling the biofilm definition.