HA when tested in cultured human synovial fibroblasts. Cells that are cultured directly from a subject are known as primary cells. Hayflick describes three phases in the life of normal cultured cells. They are capable of forming multipotent neurospheres when cultured "in vitro". If collected under sterile conditions, these cells can be further cultured, manipulated, and studied. Cell line cross-contamination can be a problem for scientists working with cultured cells. NSCs can be cultured "in vitro" as neurospheres. These agar plates provide a solid medium on which microbes may be cultured. In toxicoinfectious botulism, the organism can be cultured from tissues. Organisms may be cultured from the lesions. To prevent spawning, sterile oysters are now cultured by crossbreeding tetraploid and diploid oysters. Aspirated fluid can also be cultured to identify the infectious organism. The acidification can also come from bacterial fermentation such as in cultured milk. The bacteria are easily cultured and do not appear to cause disease. Unlike tsetse's primary symbiont "Wigglesworthia", though, "Sodalis" has been cultured "in vitro".