Phase transition of gonococci in mammalian cell cultures

Neisseria gonorrhoeae was cultivated in mammalian cell cultures in an effort to determine if this environment will elicit a T4 --> T1 transition. Of four avirulent (T4) isolates tested, only one, H4, yielded T1 colonies. This change was consistently obtained in HeLa, WI-38, and MK2 cells, even when the multiplicity of the gonococcal infection was less than 1 per culture. Growth of the gonococci took place primarily on the surface of the cells, as demonstrated by light and electron microscopy, but occasional bacteria were undoubtedly intracellular. T1 colonies were seen at 24 h and were the major population at 48 h. This shift was favored by the presence of viable cells, since smaller yields of T1 were obtained when the cells were irradiated or heat inactivated. It was also favored by low pH, since T1 recovery was reduced when the buffering capacity of the medium was increased. Although the results suggest that T1 gonococci derived from H4 have a selective advantage over T4 in cell cultures, this is not true of all T1 and T4 colony types. F62 T4, which does not undergo a T4 --> T1 shift, propagated as well as T1 in HeLa cell cultures. The change in colony type of strain H4 to T1 was accompanied by formation of pili and by gain in capacity for deoxyribonucleic acid-mediated transformation. It is concluded that gonococci can undergo T4 --> T1 phase transition in mammalian cell cultures, but this property is not retained by all strains.