What is the typical shape of a bacteriophage?

AIIMS CRE, SNO-2024

Applied Microbiology & Infection control

Easy

Appeared in: AIIMS CRE, SNO-2024

Explanation

The most common and well-studied bacteriophages have a complex structure consisting of a distinct head and a tail.
This head-and-tail morphology gives them an appearance that is best described as 'tadpole-shaped'.
The head, or capsid, contains the genetic material, while the tail and its fibers are responsible for attaching to and injecting this material into a host bacterium.

Option A: This shape is characteristic of cocci bacteria (e.g., Staphylococcus) or some animal viruses like the influenza virus, not the complex structure of a typical bacteriophage.
Option B: This shape describes bacilli bacteria (e.g., Escherichia coli) or some plant viruses. It lacks the distinct head-and-tail structure of a phage.
Option D: This shape is found in bacteria like spirilla or spirochetes (e.g., Treponema pallidum). It does not match the bacteriophage's morphology.

Visual 1: Diagram - A labeled diagram of a T4 bacteriophage, clearly showing the icosahedral head, collar, contractile sheath (tail), base plate, and tail fibers. Caption: 'Structure of a typical bacteriophage, highlighting its tadpole-like shape.'
Visual 2: Infographic - A comparative chart showing different microbial shapes: spherical (cocci), rod-shaped (bacilli), spiral (spirilla), and the complex/tadpole shape of a bacteriophage. Caption: 'Comparison of common shapes of microorganisms.'

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Morphology of Bacteriophages as background academic context rather than a clinical decision trigger.
Understanding bacteriophage structure is fundamental to microbiology and emerging fields like phage therapy.
Phage therapy uses the specificity of phages to target and destroy pathogenic bacteria, offering a potential solution to the growing problem of antibiotic resistance.
What if the question asked about a simpler phage? Some phages (e.g., filamentous or icosahedral phages) lack the classic tail structure and would not be described as tadpole-shaped. However, the 'typical' complex phage is the standard model taught and is tadpole-shaped.

How to Approach the Question

This is a factual recall question from the field of microbiology.
First, identify the core subject of the question: 'bacteriophage' and the specific attribute being asked: 'typical shape'.
Recall or visualize the classic diagram of a bacteriophage that is commonly taught. This image typically shows a structure with a distinct head and a long tail.
Compare this mental image to the given options. 'Tadpole' is the most fitting description for this head-and-tail shape.
Systematically eliminate the other options by associating them with different types of microorganisms: 'Spherical' with cocci, 'Rod-shaped' with bacilli, and 'Spiral' with spirilla or spirochetes.

Concept Tested & Keywords

QIgty-iJHVvJ30tlVr4fjr