type 1 and increased in number in the maintenance medium of cultures of L132 cells. The former mycoplasma grew slowly, but the latter grew rapidly and persisted in the cultures for more than a month. Neither mycoplasma grew in maintenance medium that had not been in contact with cells. In contrast, two T-mycoplasmas of human origin, one from the genital tract and the other from the oropharynx, grew rapidly in cultures of L132 cells and sometimes in maintenance medium from tubes without cells also, but persisted for 3–4 days only.

Even though there was growth of T-mycoplasmas in the maintenance medium of infected cell cultures, the cells contributed to the mycoplasma growth. Thus, serum-free maintenance medium alone did not support growth, but did so when used in cell cultures. Very small amounts of urea—probably derived from the cells—may have been responsible for the growth. The addition of 0·01–0·05 per cent. urea increased the number of viable T-mycoplasma organisms. In the presence or absence of additional urea, most organisms were found free in the maintenance medium overlying cell monolayers, but some were present in close association with the cells. Treatment of T-mycoplasma-infected cultures with streptomycin, which was lethal for extracellular T-mycoplasma organisms, followed by disruption of the cells, led to the release of viable organisms, indicating that some organisms were intracellular.

Minimal cytopathic changes were seen in cultures of L132, HeLa and Vero cells, particularly when 0·05 per cent. urea was added. Chronic infection could not be established in the cultures because the mycoplasmas usually died before the optimum time for cell subculture. The appearance of a T-mycoplasma inhibitor in the cultures possibly may have been partly responsible for this. The failure of T-mycoplasmas to persist in these cell cultures contrasts with their behaviour in the human host and in organ cultures.


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