of many factors (e.g. diffusion). Cell culture basal media There are different kinds of cell culture media which being used routinely in life science including the following: MEM DMEM RPMI 1640 Ham's f-12 IMDM Leibovitz L-15 DMEM/F-12 Components of cell culture media Typical Growth conditions Cell line cross-contamination Cell line cross-contamination can be a problem for scientists working with cultured cells. Studies suggest anywhere from 15 to 20% of the time, cells used in experiments have been misidentified or contaminated with another cell line. Problems with cell line cross-contamination have even been detected in lines from the NCI-60 panel, which are used routinely for drug-screening studies. Major cell line repositories, including the American Type Culture Collection (ATCC), the European Collection of Cell Cultures (ECACC) and the German Collection of Microorganisms and Cell Cultures (DSMZ), have received cell line submissions from researchers that were misidentified by them. Such contamination poses a problem for the quality of research produced using cell culture lines, and the major repositories are now authenticating all cell line submissions. ATCC uses short tandem repeat (STR) DNA fingerprinting to authenticate its cell lines. To address this problem of cell line cross-contamination, researchers are encouraged to authenticate their cell lines at an early passage to establish the identity of the cell line. Authentication should be repeated before freezing cell line stocks, every two months during active culturing and before any publication of research data generated using the cell lines. Many methods are used to identify cell lines, including isoenzyme analysis, human lymphocyte antigen (HLA) typing, chromosomal analysis, karyotyping, morphology and STR analysis. One significant cell-line cross contaminant is the immortal HeLa cell line. Hela contamination was first noted in the early 1960s in non-human culture in the USA. Intraspecies contamination was discovered in nineteen cell lines in the seventies. In 1974, five human cell lines from the Soviet Union were found to be Hela. A follow-up study analysing 50-odd cell lines indicated that half had Hela markers, but contaminant Hela had hybridised with the original cell lines. Hela cell contamination from air droplets has been reported. Hela was even unknowingly injected into human subjects by Jonas Salk in a 1978 vaccine trial. Other technical issues As cells generally continue to divide in culture, they generally grow to fill the available area or volume. This can generate several issues: Nutrient depletion in the growth media Changes in pH of the