In which condition does the proportion of cocci decrease in biofilm?

The correct choice is tied to the dynamics of biofilm development and changes in the microbial composition over time. As biofilms mature, the structure and population of microorganisms within them evolve significantly. Initially, when a biofilm forms on a surface, it is often populated by cocci, which are round bacteria that can proliferate quickly. However, as the biofilm ages, environmental conditions and nutrient availability change. This maturation leads to the growth of more complex forms of bacteria, such as rods and spirochetes, which can replace some of the cocci.

This transition is crucial because mature biofilms typically have a more diverse microbial community that includes a wider array of bacterial species. These changes in proportion are influenced by factors such as competition for resources, metabolic byproducts, and interactions among the microbes in the biofilm. Therefore, the decrease in cocci in an aging biofilm signifies a shift towards a more complex, typically more resilient microbial community that is better adapted to its environment.

The other options pertain to different scenarios that may influence biofilm composition but do not specifically address the natural progression of microbial evolution in an aging biofilm. For instance, brushing teeth disrupts the biofilm mechanically but does not necessarily lead to a decrease in cocci