Morphological and Quantitative Aspects of Mycoplasma-Human Cell Relationships.

Summary Microscopic observations of my-coplasma-mfected FL human amnion cells exposed to hypotonic treatment, air drying, and staining with orcein according to the procedure previously reported, have yielded new information concerning the morphology and quantitative relationships between myco-plasma and mammalian cells. At lower levels of infection amounts of mycoplasma per cell can be determined by actual counts; for more heavily infected cultures according to defined degrees. There is a correlation, independent of the incubation period (within limits), between the quantity of cell-associated mycoplasma and mycoplasma titer (colony-forming units per ml) in the cell culture fluid. Maximum value of this titer increases gradually with the number of FL cells per culture. Increase of cell-associated mycoplasma with time is logarithmical. The amount per FL cell (other factors equal) increases with decreasing number of FL cells demonstrating that the mycoplasma compete for cell-association and are not randomly distributed in the culture. Cell-attached mycoplasma are also observed earliest in cultures containing low numbers of FL cells. Under such conditions mycoplasma (of strain HT) can be seen on cells within 2 hours after an inoculum of 3 × 105 colony-forming units. The proportion of free to cell-associated mycoplasma varied, in one experiment, between 400:1 and 16:1. At temperatures lower than 37°C (30°C, 24°C) this proportion increases.