INTRACELLULAR GROWTH AND TYPE VARIATION O F

EVEN today the cultivation of Neisseria gonorrhoeae on laboratory media may present difficulties. Despite a wide range of media, including those containing ascitic fluid or other native protein, the long-term cultivation of gonococci without spontaneous degradation to avirulent forms is almost impossible. The gonococcus can be maintained in a fully virulent form only by the selective transfer of type I (virulent) colonies (Kellogg et al., 1963). The failure to infect small laboratory animals with the gonococcus has limited research, especially into the immune response of the host and the in-vivo behaviour of the organism. However, these disadvantages have been partly overcome by the use of tissue-culture cells to study the reactions of the cell to N. gonorrhoeae and the subsequent sensitivity of engulfed organisms to antibiotics (Thayer et al., 1957; Meyer-Rohn and Rohde, 1961; Rohde and Meyer-Rohn, 1961). Long-term cultivation, in which the gonococcus sur-viyed up to 88 days has been reported by Gavrilescu et al. (1966), who used a KB cell-line, Diena et al. (1971) developed a technique for assay of the anti-bacterial action of serum antibody against the gonococcus; they used monkey-kidney cells infected with gonococci as an indicator system. Kenny and Aris (1969) claimed that after growth for 48 hr in monkey-kidney tissue cultures, avirulent gonococci of types I11 and IV (Kellogg et al.) subcultured on labora-tory medium yielded colonies of virulent types I and 11. We have studied the growth and stability of colonial types I and IV gono-cocci in mouse (3T3) and monkey (Vero and LLC-MK2) tissue-culture cells