A subculture is a new culture prepared by transferring microorganisms or cells from a previous culture to fresh growth medium to maintain viability or isolate a specific strain.
Explanation
In microbiology and cell biology, subculturing is an essential technique for sustaining growth and obtaining pure cultures. As cells consume nutrients and produce waste, the original medium becomes depleted and toxic, leading to stationary phase or cell death. By aseptically transferring a portion of the culture to fresh medium, nutrients are replenished and organisms continue to multiply. Subculturing also allows separation of individual species from mixed cultures by selecting single colonies and re‑plating them. For adherent mammalian cell lines, the process is often called passaging: cells are detached using enzymes such as trypsin, diluted, and seeded into new flasks before they reach confluence to prevent contact inhibition and senescence. Subculturing must be performed under sterile conditions to avoid introducing contaminants, and documentation of passage number is important because prolonged passaging can select for mutations or phenotypic changes. Regular subculture helps maintain strain viability for research, diagnostics and industrial applications.
Practical applications
After streaking a mixed broth on an agar plate, a microbiologist picks a single colony and subcultures it onto another plate to obtain a pure isolate for identification or antimicrobial susceptibility testing. In medical laboratories, blood cultures that become positive are subcultured onto different agar media to recover bacterial and fungal pathogens. In tissue culture, HeLa cells may be passaged every few days into fresh medium to maintain exponential growth. Subculturing of fungal isolates allows selection of a single spore for genetic studies. These practices extend the life of cultures and ensure that results reflect the properties of a single organism or cell line.
Subculturing is a routine yet critical practice that keeps cultures healthy, enables isolation of pure strains and supports reproducible research.
Related Terms: Passage, Pure culture, Streaking, Inoculum, Culture medium