Advanced Dental Admission Test (ADAT)

What is the morphological characteristic of Streptococcus pneumoniae?

1. Bacilli structure

2. Lance-shaped diplococci

3. Chains of cocci

4. Coagulase-positive clusters

The correct answer is: Lance-shaped diplococci

Streptococcus pneumoniae is characterized by its unique morphological structure, which is identified as lance-shaped diplococci. This bacterium typically appears in pairs (diplococci) and is often described as having a lance or almond shape, which distinguishes it from other cocci that may appear round or in different arrangements. Unlike bacilli, which are rod-shaped, the shape of Streptococcus pneumoniae is indicative of its classification within the cocci group. The arrangement as diplococci reflects how these bacteria tend to divide and remain attached in pairs post-fission. They do not form long chains, so the concept of chains of cocci is not applicable to this organism. Additionally, coagulase-positive clusters are specific to different bacterial species, primarily staphylococci, and have no relevance to the morphology of Streptococcus pneumoniae. Thus, understanding these morphological characteristics is essential for identifying this pathogen, which is a significant cause of pneumonia and other infections.