04 Cell Culture and Aseptic Technique

What cell culture requires

Cell culture is the growth of microorganisms, plant tissues, or animal cells under controlled conditions outside their natural environment. Successful growth requires suitable nutrients, temperature, pH, gas exchange, and moisture. The appropriate conditions vary with the organism or cell type.

Preventing contamination

Aseptic technique reduces the chance that unwanted organisms or cells will enter a culture, but it does not guarantee a completely sterile workspace. Contaminants can come from people, air, surfaces, tools, reagents, or other cultures. Bacteria and fungi may grow visibly, while contaminants such as mycoplasma can be difficult to detect without specific testing. Contamination can alter growth and experimental results or destroy a culture.

Good practice includes preparing a clean, organized work area; using appropriate protective equipment and sterile supplies; opening culture vessels only when needed; and avoiding contact between sterile items and nonsterile surfaces. Keep containers closed when not in use, label them clearly, and handle one culture at a time to reduce mix-ups and cross-contamination. Use equipment suited to the work and follow institutional procedures for disinfection, waste disposal, and biological safety. Required safeguards depend on a risk assessment of the organism or material being handled.

Choosing culture media

A culture medium supplies nutrients and helps maintain conditions needed for growth. Its composition depends on the organism or cell type and the purpose of the culture. Media may be liquid or solidified with an agent such as agar. Aseptic preparation and storage matter because contamination introduced with a medium can spread to every culture that receives it.

Microbial media

Microorganisms differ in their nutritional and environmental needs. A general-purpose medium supports many organisms, while an enriched medium includes additional nutrients for organisms with more demanding requirements. A defined medium has known chemical ingredients; a complex medium contains ingredients such as extracts or digests whose exact composition is not fully specified. Selective media inhibit some organisms while favoring others. Differential media make visible differences in how organisms grow or use particular substances; for example, a color indicator may reveal a metabolic reaction.

Plant media

Plant tissue culture grows plant cells, tissues, or organs in vitro. These materials, when taken from a donor plant, are often called explants. Plant media commonly contain mineral nutrients, vitamins, a sugar source, and plant growth regulators. A gelling agent can support explants, while liquid media can provide close contact with nutrients. Murashige and Skoog (MS) medium is a widely used starting formulation, but the best recipe depends on the species, tissue, and growth stage. The balance of auxins and cytokinins can influence whether cultured tissue forms callus, shoots, or roots.

Animal-cell media

Animal cells generally need a balanced basal medium containing salts, amino acids, vitamins, and an energy source. Depending on the cell type, the medium may also need serum or defined supplements such as growth factors and hormones. Buffering helps keep pH within a suitable range; some systems rely on bicarbonate and a controlled carbon-dioxide atmosphere. Medium, temperature, gas conditions, and the need for an attachment surface are specific to the cell line, so follow established guidance for the particular culture.

Maintaining cultures

Cultures grow at different rates and in different forms. Microbes may grow as suspended cells, colonies on solid medium, or biofilms on surfaces. In a batch culture, nutrients are gradually used and waste products accumulate. Growth commonly passes through lag, exponential, stationary, and decline phases. Transfers into fresh medium can maintain a culture, but growth conditions and transfer timing should match the organism and purpose.

Plant cultures may be maintained as explants, callus, shoots, or cell suspensions. Subculture moves growing material onto fresh medium before nutrients are depleted or growth becomes unsuitable. In micropropagation, cultures can move through stages for establishment, multiplication, rooting, and acclimatization to conditions outside the culture vessel.

Animal cultures may grow attached to a surface as a monolayer or in suspension. Attached cells are passaged by detaching and transferring them to fresh vessels; suspension cultures are maintained by transferring an appropriate portion into fresh medium. Passage timing and seeding density influence growth and cell behavior. Record culture identity, passage number, dates, and relevant observations so changes can be traced.

Monitoring culture health

Routine observation helps identify healthy growth and problems early. Check cultures for expected appearance and growth, and monitor for signs of contamination or changes in medium. Visual inspection alone cannot rule out all contaminants, so use appropriate testing and authentication practices where needed.

Antibiotics should not substitute for aseptic technique. They can mask contamination, affect cells, or select for resistant organisms. Appropriate handling, maintenance, records, and monitoring help protect culture quality and make results more reliable.

• Explant