What is the difference between a bacterium and a mycoplasma?

Question

The other day our teacher asked what makes mycoplasma different from typical bacteria, and I realized it’s not just one thing but a whole list. I later looked it up and found out how unique they are—like not even having a cell wall. This post clears up the key differences with real examples and why they matter in medicine and microbiology labs.

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Anttilampinen 2025-06-13T12:13:38+00:00 1 Answer 7 views
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Answer ( 1 )

  1. fleming
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    2025-07-13T14:53:03+00:00
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    Short answer

    Mycoplasmas are bacteria, but they are cell‑wall‑less, tiny and highly fastidious, so they behave quite differently from the garden variety walled bacteria.

    Key differences

    • Cell wall: Typical bacteria have a peptidoglycan wall; mycoplasmas have none. They stabilise their plasma membrane with sterols borrowed from the host.
    • Shape: Without a rigid wall they are pleomorphic – filaments, coccoid bodies, anything goes.
    • Size: Among the smallest free‑living organisms (~0.2–0.3 μm) and can slip through 0.45 μm filters.
    • Staining: Do not retain Gram stain because the dye binds to peptidoglycan.
    • Growth requirements: Need cholesterol and rich media; grow slowly forming the classic “fried‑egg” colonies on PPLO agar.
    • Antibiotic susceptibility: Naturally resistant to beta‑lactams and other wall inhibitors; sensitive to macrolides, tetracyclines and fluoroquinolones.
    • Genome: Very small (~0.6 Mb) with many metabolic pathways missing, so they rely on host nutrients.

    What stays the same

    They still have bacterial ribosomes, replicate by binary fission and are inhibited by antibiotics that target protein or DNA synthesis.

    Why it matters

    The lack of a wall means you must choose antibiotics that hit targets other than peptidoglycan, and it explains why mycoplasmas can slip through filters and contaminate cell cultures.

    Hope that helps, shout if anything still unclear.

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