Behavior of Mycoplasma hominis in a Human Diploid Cell Culture System

The behavior of Mycoplasma hominis in normal human embryonic lung fibroblast (HAIN‐55) cell cultures was investigated. Multiplication patterns of cell‐associated mycoplasmas and of extracellular mycoplasmas in the HAIN‐55 cultures depended upon the size of the inoculum. This relationship did not vary with the number of days the cells had been cultured, nor with the number of HAIN‐55 cell passages. The maximum mycoplasmal growth was obtained with inoculum sizes of 105 to 106 colony‐forming units (CFU)/ml. The recovery of mycoplasmas decreased rapidly with inoculum size beyond 107 CFU/ml, and growth of the HAIN‐55 cells was inhibited. Growth of the cells was also inhibited by the addition of the cytoplasmic fraction of Mycoplasma hominis.