A contaminated culture is a microbial culture that contains unwanted organisms or impurities not part of the intended organism being studied.
Explanation
In microbiology and cell culture, maintaining purity is fundamental because mixed populations of microbes can alter experimental outcomes. Contaminated cultures often arise from inadequate sterilization of media, glassware or instruments, or from poor aseptic technique that allows microorganisms from the environment or the operator to enter the system. Bacteria, yeasts, moulds, and mycoplasmas are common contaminants. These organisms may grow faster than the desired microbe, outcompete it for nutrients, produce metabolites that inhibit growth or alter the pH of the medium.
Contamination has consequences beyond the laboratory. In clinical laboratories, contamination of blood cultures can lead to false‑positive results and misdiagnosis. In pharmaceutical production, contaminated cell cultures may compromise product safety, while in research settings they can invalidate experiments. To detect contamination, scientists monitor turbidity, colour changes, unexpected colonies on solid media, or perform microscopic examinations. Once contamination is detected, the culture is typically discarded because removing unwanted organisms without damaging the desired culture is rarely feasible.
Key Examples and Facts
- A clear bacterial broth becoming cloudy due to fungal growth is a classic sign of contamination.
- Mycoplasma contamination in mammalian cell cultures is often invisible but can alter gene expression and metabolism.
- Using non‑sterile pipette tips or leaving culture vessels open can introduce airborne spores.
- Laboratories employ laminar flow hoods, autoclaving, and strict aseptic technique to prevent contamination.
Contaminated cultures are undesirable because they compromise the reliability of experimental data and product quality. Preventing contamination through proper sterilization and handling is easier than attempting to eliminate contaminants after they appear.
Related Terms: Contamination, Culture, Pure Culture, Mixed Culture, Sterilization