What pathogen is the most important contributor to biofilms in plaque?
staphylococcus aureus
streptococcus mutans
escherichia coli
clostridium difficile

Streptococcus mutans

Explanation:

Tooth decay results from metabolic activity of the microbes which live on  teeth.  

A layer of carbohydrates and the proteins forms when the teeth which is clean come into contact with the saliva.  

Certain microbes are attracted to these biomolecular food source and thus form a biofilm which is known as plaque.  

Streptococcus mutans is the most important cariogenic species.  

When a disaccharide sugar from the food, is broken down by the bacteria in mouth, the units glucose and the fructose are produced. Glucose is used to make the dextran, which is part of extracellular matrix of biofilm. Fructose is fermented which produces organic acids which dissolve minerals of  tooth. The plaque biofilm overtime become thick and calcify eventually.