Which is an example of gram negative organisms?

RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Applied Microbiology & Infection control

Easy

Appeared in: RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Explanation

Vibrio cholerae is the causative agent of cholera, an acute diarrheal illness.
It is a comma-shaped, motile, Gram-negative rod.
Gram-negative bacteria have a distinct cell wall structure with a thin peptidoglycan layer and an outer lipopolysaccharide membrane.
During the Gram stain procedure, they lose the primary crystal violet stain and are counterstained pink or red by safranin.

Option A: Listeria monocytogenes is a Gram-positive bacillus (rod-shaped bacterium).
Option B: Streptococcus pneumoniae is a Gram-positive coccus (spherical bacterium), typically arranged in pairs.
Option D: Staphylococcus aureus is a Gram-positive coccus, characteristically found in grape-like clusters.

Visual 1: Diagram: A flowchart illustrating the steps of the Gram staining procedure (crystal violet, iodine, decolorizer, safranin) and the resulting colors for Gram-positive and Gram-negative bacteria.
Visual 2: Illustration: A comparison of the cell wall structures of Gram-positive and Gram-negative bacteria, highlighting the thick peptidoglycan layer in Gram-positive and the thin peptidoglycan layer with an outer membrane in Gram-negative.
Visual 3: Micrograph: Images showing the microscopic appearance of all four bacteria after Gram staining: purple cocci in clusters (Staphylococcus), purple cocci in pairs (Streptococcus), purple rods (Listeria), and pink/red comma-shaped rods (Vibrio).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Classification of bacteria based on Gram staining as background academic context rather than a clinical decision trigger.
Gram stain results are crucial for the initial identification of a bacterial pathogen, guiding the preliminary choice of antibiotics. Gram-negative and Gram-positive bacteria often respond to different classes of antibiotics.
For instance, the outer membrane of Gram-negative bacteria like V. cholerae can prevent certain antibiotics (like penicillin) from reaching their target, necessitating the use of alternative drugs.
Knowing an organism is Gram-negative immediately raises concerns about endotoxins (lipopolysaccharide), which can cause fever, shock, and other severe systemic reactions.

How to Approach the Question

First, understand the question. It asks to identify the Gram-negative organism from the given list.
This is a factual recall question. You need to remember the Gram stain characteristics of common pathogenic bacteria.
Systematically evaluate each option. Recall or deduce the Gram stain property for each bacterium.
Listeria, Streptococcus, and Staphylococcus are classic examples of Gram-positive bacteria.
Vibrio, along with E. coli, Salmonella, and Shigella, are classic examples of Gram-negative bacteria.
Select the option that fits the Gram-negative classification. In this case, it is Vibrio cholerae.

Concept Tested & Keywords

Q8AoZCbb5WSP1fzPzoTk4b