Which of the following laboratory tests is NOT useful for differentiating Streptococcus mutans from other oral streptococci?

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Gram stainingMannitol and sorbitol fermentation testsSynthesis of both intracellular and extracellular sticky polysaccharidesAppearance of colonies on saliva agar plates

Explanation

Gram staining does not help differentiate Streptococcus mutans from other oral streptococci because they all appear as Gram-positive cocci. However, tests such as fermentation of mannitol and sorbitol, production of adherent polysaccharides, and colony morphology on saliva agar are useful for distinguishing S. mutans.