**Core Concept**
Dental plaque formation begins with the attachment of primary bacterial colonizers to the tooth surface. These initial bacteria are gram-positive, facultative anaerobes that adhere to the tooth enamel and establish a biofilm, which eventually leads to the formation of dental plaque.

**Why the Correct Answer is Right**
The primary bacterial colonizers of the tooth in dental plaque formation are typically _Streptococcus mutans_ and _Streptococcus sanguinis_. These bacteria possess a unique ability to adhere to the tooth surface due to their hydrophobic surface properties and the presence of adhesins such as antigen I/II. They are also capable of producing extracellular polysaccharides, which contribute to the formation of a biofilm.

**Why Each Wrong Option is Incorrect**
* **Option A:** While _Actinomyces_ species are also involved in dental plaque formation, they are not the primary colonizers.
* **Option B:** _Escherichia coli_ is a gram-negative bacterium and not typically associated with the initial stages of dental plaque formation.
* **Option C:** _Fusobacterium_ species are anaerobic bacteria that colonize the oral cavity but are not the primary colonizers of the tooth surface.

**Clinical Pearl / High-Yield Fact**
The primary bacterial colonizers of the tooth surface, such as _Streptococcus mutans_, are responsible for the initiation of dental caries. Regular oral hygiene practices, including brushing and flossing, can help prevent the accumulation of these bacteria and reduce the risk of dental caries.

**Correct Answer:** C. _Fusobacterium_ species are anaerobic bacteria that colonize the oral cavity but are not the primary colonizers of the tooth surface