Which among the following bacteria lack a cell wall?

AIIMS Raipur - 2017 (Shift-3)

Applied Microbiology & Infection control

Easy

Appeared in: AIIMS Raipur - 2017 (Shift-3)

Explanation

Mycoplasma is a genus of bacteria that is unique because it naturally lacks a cell wall around its cell membrane.
This absence of a rigid peptidoglycan layer makes Mycoplasma pleomorphic (variable in shape) and resistant to common antibiotics like penicillin that act by inhibiting cell wall synthesis.
Due to their lack of a cell wall, they are not visible on a Gram stain.
They are considered the smallest free-living microorganisms.

Option B: Spirochetes possess a thin peptidoglycan cell wall located in the periplasmic space, which contributes to their flexible, spiral shape.
Option C: Actinomycetes are Gram-positive bacteria that have a thick cell wall and are known for their filamentous, branching growth pattern.
Option D: Vibrios are Gram-negative bacteria that have a standard cell wall structure, including a thin peptidoglycan layer and an outer membrane.

Visual 1: Diagram: Comparison of a typical bacterial cell (with a cell wall) and a Mycoplasma cell (without a cell wall), highlighting the structural differences.
Visual 2: Infographic: Illustrating the mechanism of action of penicillin on a bacterial cell wall and explaining why it is ineffective against Mycoplasma.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Bacterial morphology and cell wall characteristics as background academic context rather than a clinical decision trigger.
Knowing that Mycoplasma lacks a cell wall is critical for antibiotic selection. Beta-lactam antibiotics (e.g., penicillin, cephalosporins) are ineffective. Treatment requires drugs that target other processes, such as protein synthesis (e.g., macrolides, tetracyclines).
Mycoplasma infections, like atypical pneumonia ('walking pneumonia'), often present with different symptoms than typical bacterial pneumonia, and this knowledge guides diagnosis and treatment.
What if? If a patient with suspected pneumonia does not respond to a course of amoxicillin, a nurse should consider the possibility of an atypical pathogen like Mycoplasma and anticipate the physician may switch to an antibiotic like azithromycin.

How to Approach the Question

This is a factual recall question from microbiology.
First, identify the core concept being tested: the presence or absence of a cell wall in different types of bacteria.
Recall the major classifications and unique characteristics of bacteria. Mycoplasma is famously known as the primary exception for naturally lacking a cell wall.
Evaluate each option based on this knowledge. Spirochetes, Actinomycetes, and Vibrios are all known bacterial forms that possess a cell wall, although their structures may vary.
Select the option that is the well-established exception to the general rule that bacteria have cell walls.

Concept Tested & Keywords

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