Maintenance of virulent gonococci in laboratory culture.

Abstract

WE have previously shown1 that gonococci in urethral exudates are resistant to the bactericidal action of complement plus natural or immune antibodies, yet after subculture the same strains are rapidly killed. Earlier workers2 could infect volunteers more readily with gonococci from urethral pus than with the same strains grown in the laboratory. Together, these findings suggest that on subculture gonococci may lose both virulence and resistance to serum killing in parallel. Nevertheless, Kellogg et al.3, 4 believe that gonococci can be maintained in a virulent form on culture and that the virulent can be distinguished from avirulent forms by their different colonial morphology on their colonial type medium (CT medium). Freshly isolated gonococci had colony types referred to as 1 and 2; on random subculture different colonies known as types 3 and 4 appeared. Even after repeated subculture one strain, F62, in the type 1 colony form was able to infect volunteers, whereas the so-called avirulent type 4 colonies had lost this ability after some sixty-nine passages in vitro. Nevertheless the dose of type 1 organisms needed to set up infection was about 1.5 × 1010 microbes5. These results need not conflict with our1 impression that virulence, if correlated with resistance to antibody plus complement, is lost after even one subculture. If one postulates that loss of virulence occurs in two steps type 1 organisms might be phenotypically avirulent while the type 4 colonies might have actually lost the genetic information required for virulence. The vast dose used to challenge volunteers would enable a few gonococci to survive in the host long enough to revert to the phenotypically virulent form.