The extra – cellular polysaccharide synthesized by cariogenic streptococci in the presence of excess sucrose are best described as
Cariogenic streptococci, like Streptococcus mutans, are known for causing dental caries. The key here is the extracellular polysaccharides. These bacteria use enzymes to convert sucrose into sticky polysaccharides that help them adhere to teeth and form biofilms, which are plaque. The primary enzyme involved is glucosyltransferase (GTF), which polymerizes glucose from sucrose into glucans.
So the correct answer should be "Glucans." Now, the options aren't provided, but common distractors might include other types of polysaccharides like fructans, which are made by other bacteria, or maybe something like dextran, which is a form of glucan. Also, options might confuse the enzymes with the products, like GTF itself instead of the polysaccharide.
Wrong options would likely include fructans (made by other bacteria using fructosyltransferase), dextrans (which are similar but maybe a different classification), or maybe even something like lipopolysaccharides, which are cell wall components not related to sucrose metabolism. Each incorrect option should be explained based on their production mechanism or function.
The clinical pearl here is that glucans are crucial for biofilm formation, leading to dental caries. Students should remember that S. mutans uses sucrose to make these sticky polymers, which are a key part of plaque formation.
**Core Concept**
Cariogenic streptococci, particularly *Streptococcus mutans*, synthesize extracellular glucans from sucrose using glucosyltransferase (GTF) enzymes. These glucans form a sticky matrix that facilitates biofilm adherence to tooth surfaces, promoting dental caries.
**Why the Correct Answer is Right**
Glucans are linear or branched polymers of glucose, synthesized by GTF enzymes in the presence of sucrose. They act as adhesives for bacterial colonization and create a protective environment for acid production, leading to enamel demineralization. The process involves sucrose hydrolysis by GTF to generate glucose units, which are polymerized into insoluble glucans.
**Why Each Wrong Option is Incorrect**
**Option A:** *Fructans* are synthesized by fructosyltransferases in other bacteria (e.g., *Streptococcus sobrinus*), not cariogenic streptococci.
**Option B:** *Dextrans* are glucan derivatives but are typically produced by *Lactobacillus* species or fungal *Leuconostoc*, not *S. mutans*.
**Option C:** *Lipopolysaccharides* are endotoxins from Gram-negative bacteria, unrelated to sucrose metabolism.
**Clinical Pearl / High-Yield Fact**
"**GTF → Glucans → Plaque → Caries**" is a critical pathway in dental pathology. S. mutans’ ability to synthesize glucans from sucrose is a