Effects of Mycoplasma hominis on in-vitro studies of Neisseria gonorrhoeae.

This study examined the effects Mycoplasma hominis might have on Neisseria gonorrhoeae. Two auxotype standard strains of N. gonorrhoeae were found by culture and by light, fluorescence, and electron microscopy to be contaminated with M. hominis. In the presence of M. hominis, these strains of N. gonorrhoeae were typed as prototrophic. Removal of the mycoplasmas by passage of the N. gonorrhoeae on serum-free medium resulted in a second change in growth requirements rather than a reversion to the initial auxotypes. For one of these gonococcal strains, the presence of M. hominis also coincided with a change in colonial morphology and the appearance of a 2.6 X 10(6)-dalton plasmid, changes which persisted after the mycoplasmas had been eliminated from the culture of N. gonorrhoeae. The plasmid was not detected in a pure culture of the M. hominis strain or when it and the N. gonorrhoeae strain were intentionally co-cultivated. While these findings cannot be fully explained, they emphasize the importance of ensuring that all strains of N. gonorrhoeae used for in vitro studies are free of mycoplasmas.