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Oral Microbiology — NDEB AFK MCQ

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EasyBiomedical SciencesOral MicrobiologyNDEB AFK

A Gram-positive, catalase-negative coccus arranged in chains is isolated from a subgingival plaque sample. Which organism does this most likely represent?

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Correct answer: D — Streptococcus species

Gram-positive, catalase-negative cocci in chains are characteristic of Streptococcus species. Staphylococcus is Gram-positive but catalase-positive and typically arranged in clusters. Neisseria is Gram-negative diplococci. E. coli is a Gram-negative rod. P. gingivalis is a Gram-negative anaerobic rod associated with periodontal disease.

Reference: Lamont – Oral Microbiology and Immunology, 3rd ed., 2019