Question

Although not required for cell growth, antibiotics are one of the most essential components of animal cell culture medium. Why? Give examples of two such antibiotics often used in animal cell culture medium.

Hint:

While antibiotics protect cell cultures, their long-term use is discouraged because they can mask low-level contamination (like mycoplasma), alter cell gene expression, and encourage the selection of drug-resistant microbial strains.

Answer 1

Step 1: Concept
Animal cell cultures are highly susceptible to contamination by microscopic pathogens like bacteria, fungi, and mycoplasma.

Step 2: Why Antibiotics are Essential
Unlike bacteria, which can divide every 20 minutes, animal cells grow slowly, typically dividing once every 18 to 24 hours. - If a single bacterial cell or fungal spore enters a culture flask, it will rapidly consume nutrients and completely outgrow the slower-dividing animal cells within 24 hours, producing toxic waste products that kill the animal cells.
- Because animal cells lack a cell wall, they are highly sensitive to metabolic toxins.
- Antibiotics are added to animal cell culture media to prevent or eliminate microbial contamination, keeping the culture sterile during growth.


Step 3: Common Examples
The most commonly used antibiotics in animal cell culture are:
1. Penicillin: Active against Gram-positive bacteria (inhibits peptidoglycan cell wall synthesis).
2. Streptomycin: Active against Gram-negative bacteria (binds to the 30S ribosomal subunit to inhibit protein synthesis).
(Note: A mixture of Penicillin and Streptomycin, called "Pen-Strep", is widely used in laboratories). 3. Gentamicin: A broad-spectrum aminoglycoside antibiotic.
Final Answer: Antibiotics prevent the overgrowth of fast-dividing bacteria and fungi that would otherwise contaminate and destroy slow-growing animal cell cultures. Common examples are Penicillin and Streptomycin.