Which microorganism cannot be cultivated on artificial cell-free media?

Which microorganism cannot be cultivated on artificial cell-free media?

• A. Chlamydia trachomatis
• B. Mycoplasma hominis
• C. Mycoplasma pneumoniae
• D. Ureaplasma urealyticum

Answer: (A)

The key idea is that some bacteria cannot grow outside living cells because they rely entirely on the host cell’s machinery. Chlamydia trachomatis is an obligate intracellular parasite, meaning its replication cycle occurs inside host cells. Outside of those cells, in cell-free artificial media, it cannot multiply because it lacks the necessary metabolic processes and energy sources. Therefore, it must be cultured in living cells (or in embryonated eggs), not on standard or specialized cell-free media. In contrast, the other organisms listed are capable of growing on artificial, cell-free media when the nutrients and supplements are appropriate. Mycoplasmas and ureaplasmas are cell-wall–deficient bacteria that require enriched, lipid-containing media, but they do not strictly need host cells for replication and can be cultured outside cells with the right formulations. This is why they are not restricted to intracellular growth like Chlamydia. So, the organism that cannot be cultivated on artificial cell-free media is Chlamydia trachomatis.

The key idea is that some bacteria cannot grow outside living cells because they rely entirely on the host cell’s machinery. Chlamydia trachomatis is an obligate intracellular parasite, meaning its replication cycle occurs inside host cells. Outside of those cells, in cell-free artificial media, it cannot multiply because it lacks the necessary metabolic processes and energy sources. Therefore, it must be cultured in living cells (or in embryonated eggs), not on standard or specialized cell-free media.

In contrast, the other organisms listed are capable of growing on artificial, cell-free media when the nutrients and supplements are appropriate. Mycoplasmas and ureaplasmas are cell-wall–deficient bacteria that require enriched, lipid-containing media, but they do not strictly need host cells for replication and can be cultured outside cells with the right formulations. This is why they are not restricted to intracellular growth like Chlamydia.

So, the organism that cannot be cultivated on artificial cell-free media is Chlamydia trachomatis.