Q.2 Which one of the following statements is CORRECT for Mycoplasma?

Mycoplasma lack a cell wall, making them resistant to cell wall-targeting antibiotics like penicillin while exhibiting pleomorphic shapes, sensitivity to osmotic shock, and pathogenic potential in humans.

Option Analysis

Option (A) Their cells are of definite shape.
Mycoplasma cells lack a rigid cell wall, resulting in pleomorphic or variable shapes such as spherical, filamentous, or irregular forms that change with environmental conditions. This statement is incorrect.

Option (B) They are resistant to lysis by osmotic shock.
Without a cell wall, Mycoplasma cells rely solely on their plasma membrane, rendering them sensitive to osmotic lysis rather than resistant. Some sources note variability, but standard characterization confirms sensitivity. This statement is incorrect.

Option (C) Their growth is not inhibited by penicillin.
Penicillin targets peptidoglycan synthesis in bacterial cell walls, which Mycoplasma completely lack, so their growth proceeds unaffected. This statement is correct.

Option (D) They are nonpathogenic to human.
Species like Mycoplasma pneumoniae cause respiratory infections such as atypical pneumonia, while others like M. genitalium lead to urogenital diseases. This statement is incorrect.

Introduction: Unraveling Mycoplasma Characteristics for CSIR NET Success
Mycoplasma characteristics reveal unique prokaryotes without cell walls, showing penicillin resistance, osmotic shock sensitivity, indefinite cell shapes, and human pathogenicity—key topics for CSIR NET Life Sciences aspirants mastering molecular biology and microbiology.

Key Mycoplasma Traits

Mycoplasma, the smallest self-replicating bacteria, belong to class Mollicutes and feature a triple-layered plasma membrane rich in sterols instead of peptidoglycan.

• Pleomorphic cells vary from spherical (0.3-0.8 µm) to branched filaments, lacking definite shape due to no rigid wall.

• Sensitive to osmotic shock as membrane alone cannot withstand hypotonic conditions.

• Inherently resistant to penicillin and beta-lactams targeting cell wall synthesis.

Penicillin Resistance Mechanism

Absence of cell wall peptidoglycan makes Mycoplasma growth unaffected by penicillin, unlike walled bacteria.
Such resistance extends to cephalosporins; instead, tetracyclines, macrolides like erythromycin, or quinolones target protein synthesis or other pathways.
This trait underscores their distinction in antibiotic susceptibility profiles.

Pathogenicity in Humans

Contrary to nonpathogenic claims, Mycoplasma species infect humans: M. pneumoniae causes walking pneumonia via epithelial adherence and toxin release.
M. genitalium links to urethritis; both evade immunity through antigenic variation.
Fried-egg colonies on agar aid diagnosis.

Exam Relevance for CSIR NET

For competitive exams like CSIR NET, focus on Mycoplasma’s wall-less nature explaining penicillin resistance (correct choice) over incorrect options like definite shape or osmotic resistance.
Master these for microbiology, biotechnology sections.