Q.67 Which one of the following organisms has axial filaments?
(A) Mycobacterium tuberculosis
(B) Pasteurella multocida
(C) Treponema pallidum
(D) Shigella dysenteriae

Treponema pallidum is the organism with axial filaments. These unique structures enable corkscrew motility in spirochetes, distinguishing it from the other options.​

Axial Filaments Explained

Axial filaments consist of flagella-like structures wrapped around the cell body of spirochetes, located between the inner cytoplasmic and outer membranes. They rotate to produce a twisting motion for navigating viscous environments like mucus or tissues. This periplasmic flagella arrangement is exclusive to spirochetes and absent in rod-shaped bacteria.​

Option Analysis

• (A) Mycobacterium tuberculosis: This rod-shaped bacterium causing tuberculosis lacks flagella or axial filaments; it shows non-motile growth with a waxy cell wall.​

• (B) Pasteurella multocida: A Gram-negative coccobacillus linked to animal diseases, it relies on capsule and LPS for virulence but has no axial filaments or typical motility structures.​

• (C) Treponema pallidum: The syphilis-causing spirochete features axial filaments (2 per cell end) that drive its characteristic corkscrew motility, confirmed by electron microscopy.​

• (D) Shigella dysenteriae: This dysentery pathogen is typically non-motile or uses peritrichous flagella under specific conditions, without axial filaments.​

Article:

Introduction to Organisms Has Axial Filaments

In microbiology, particularly for CSIR NET Life Sciences, understanding bacterial motility structures like axial filaments is crucial. The question “which one of the following organisms has axial filaments?” tests knowledge of spirochete anatomy among pathogens like Mycobacterium tuberculosis, Pasteurella multocida, Treponema pallidum, and Shigella dysenteriae. Treponema pallidum stands out due to its unique axial filaments enabling stealthy tissue invasion.​

What Are Axial Filaments?

Axial filaments are endo-flagella in spirochetes, coiled around the protoplasmic cylinder within the periplasmic space. Unlike external flagella, they drive corkscrew propulsion by rotating the outer sheath, aiding survival in host tissues. Found exclusively in spirochetes, they measure 13-21 nm in diameter.​

Detailed Option Breakdown

Treponema pallidum’s axial filaments, confirmed via ultrastructural studies, insert at cell poles and facilitate syphilis dissemination.​

CSIR NET Exam Relevance

This MCQ highlights bacterial classification: spirochetes (axial filaments) vs rods (peritrichous or none). Master it alongside flagella types for microbiology sections.​