All are gram positive cocci, EXCEPT?

Appeared in: CGHS SSC - 2018

Explanation

The question asks to identify the bacterium that is NOT a Gram-positive coccus.
Neisseria is the correct answer because it is a Gram-negative coccus, meaning it does not retain the crystal violet stain and appears pink/red.
The other three options—Pneumococcus, Streptococcus, and Staphylococcus—are all classic examples of Gram-positive cocci, which stain purple.

Option A: Pneumococcus, also known as Streptococcus pneumoniae, is a classic example of a Gram-positive coccus. It fits the criteria the question asks to exclude.
Option B: Streptococcus species are Gram-positive cocci that typically form chains. They fit the criteria the question asks to exclude.
Option D: Staphylococcus species are Gram-positive cocci known for arranging in grape-like clusters. They fit the criteria the question asks to exclude.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Gram stain classification of bacteria as background academic context rather than a clinical decision trigger.
The Gram stain is one of the most important initial tests performed on a bacterial specimen. The result (positive or negative, cocci or bacilli) provides critical information that helps clinicians make an educated guess (empiric therapy) about the appropriate antibiotic to use while waiting for definitive culture and sensitivity results.
For example, if a Gram stain of cerebrospinal fluid (CSF) shows Gram-negative diplococci, a diagnosis of meningococcal meningitis (caused by Neisseria meningitidis) is strongly suspected, and treatment with antibiotics like ceftriaxone is initiated immediately.
What if the question was 'All are Gram-negative bacteria, EXCEPT?' In that case, you would look for the one Gram-positive organism among the options. The principle of identifying the outlier remains the same.

How to Approach the Question

First, identify the core concept being tested: bacterial classification, specifically using the Gram stain.
Notice the keyword 'EXCEPT'. This signals that you are looking for the option that is different from the others. Three options will share a common characteristic, and one will be the outlier.
The shared characteristic is 'gram positive cocci'. Your task is to find the option that is NOT a Gram-positive coccus.
Evaluate each option based on your knowledge of microbiology:
Is Pneumococcus a Gram-positive coccus? Yes.
Is Streptococcus a Gram-positive coccus? Yes.

Concept Tested & Keywords

Concept Tested: Gram stain classification of bacteria
Stem keywords: gram positive cocci
Lead-in keywords: EXCEPT
Negative lead-in flag: The question uses negative framing ('EXCEPT'), asking to identify the option that does not fit the given criteria.

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E6 Microbiology Applied AnjuDhir 3e Part 1 pp. 54-56, 126-128

E6 Medicine Harrison 22e Part 1 p. 1228-1230

Practise the full CGHS SSC - 2018

Attempt every question from this paper in a timed mock, then review the full solution for each one.