Bacteria found in two days old plaque is:

# Predominant bacteria found in two days old plaque is:
A. Streptococci
B. Bacteroides
C. Spirochetes
D. Actinomyces

The correct answer is: A. Streptococci. 

- Plaque can be defined as a complex microbial community, with greater than 10^10 bacteria per milligram. 

- The formation of pellicle is the first step in plaque formation.

- "Primary colonizers" : The pellicle coated tooth surface is colonized by Gram- Positive aerobic cocci bacteria such as Streptococcus sanguis, Streptococcus mutans, and Actinomyces viscous. 

- Secondary colonizers: After 1 to 3 days, the secondary colonizers are gram negative anerobic rods and filaments that include Fusobacterium nucleatum, Prevotella intermedia, and Capnocytophaga species. 

Tertiary colonizers: After one week of plaque accumulation, other gram negative species may also be present in plaque. They include Porphyromonas gingivalis, Campylobacter rectus, Eikenella corrodens, Actinobacillus actinomycetemcomitans, and the oral spirochetes (Treponema species).

- The structural characteristics of dental plaque in this time period reveal complex patterns of bacterial cells of cocci, rods, fusiform, filaments, and spirochetes. 

- Particular specific associations of different bacterial forms have been observed . For example, the adherence of cocci to filaments results in a typical form referred to as "test tube brushes" or "corn cob" arrays. 

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