Question

The serum in mammalian cell culture medium stimulates cell growth and attachment. However, it must be filter sterilized prior to use to

• A. Removal of mycoplasma
• B. Removal of proteins
• C. Removal of collagen
• D. Removal of foaming agents

Hint:

Always use a $0.1\ \mu\text{m}$ pore size filter instead of a $0.22\ \mu\text{m}$ filter when sterilizing biological fluids like serum to ensure complete removal of wall-less Mycoplasma species.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Animal cell culture media are typically supplemented with animal serum, such as fetal bovine serum (FBS), to provide essential growth factors, hormones, and attachment proteins.
Because serum is a biological product derived from animal blood, it is a potential source of microbiological contamination.
Standard sterilization techniques like autoclaving (moist heat) cannot be used for serum because heat denatures the essential proteins and growth factors.
Therefore, membrane filtration is used to sterilize the serum before adding it to cell culture media.

Step 2: Detailed Explanation:
Filtration is a physical separation method that removes particulate matter and microorganisms based on pore size.
While standard bacterial filtration uses membranes with a pore size of $0.22\ \mu\text{m}$, some small bacteria can pass through these pores.
Mycoplasma species are the smallest known free-living self-replicating prokaryotes, ranging in size from $0.15\ \mu\text{m}$ to $0.3\ \mu\text{m}$.
Because they lack a rigid peptidoglycan cell wall, they are highly flexible and can easily deform to pass through standard $0.22\ \mu\text{m}$ sterile filters.
Mycoplasma contamination is a major issue in mammalian cell culture because it alters cell metabolism, growth rates, and gene expression without causing obvious turbidity.
To prevent this contamination, serum is sterilized using specialized filtration protocols, often involving sequential filtration through membranes with pore sizes down to $0.1\ \mu\text{m}$.
This fine filtration is specifically designed to retain and remove mycoplasma species while preserving the functional proteins of the serum.

Step 3: Final Answer:
The primary reason for filter sterilizing serum is the removal of mycoplasma contaminants.