Which of the following is an example of a biofilm?

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

Answer: (A)

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: check if the microorganisms are attached to a surface and living in a community with EPS.
3. Option 1: 'Dental plaque on teeth' fits the biofilm definition because it is a community of bacteria attached to the tooth surface within a matrix.
4. Option 2: 'A virus infecting a host cell' is not a biofilm because it involves a virus inside a cell, not a microbial community on a surface.
5. Option 3 and 4: 'A pure colony of bacteria on an agar plate' and 'A single E. coli cell in liquid culture' are not biofilms since they do not represent a community embedded in a matrix on a surface.