Pathogenesis and immunology of experimental gonococcal infection: virulence of colony types of Neisseria gonorrhoeae for chicken embryos.

The virulence of gonococcal strains and colony types was evaluated in embryonated hen eggs of various ages inoculated by different routes. Striking differences in virulence of colony types were revealed by intravenous inoculation of 11-day embryos. T1 and T2 colony types were found to have high virulence for embryos, whereas T3 and T4 colony types were relatively avirulent. These observations are in accord with previous studies in volunteers. The differences in virulence were not related to differences in toxicity of killed gonococci, sonic lysates, or to the susceptibility of gonococci to cidal effects of chicken embryo blood. Rather, they appeared to involve differences in clearance of gonococci from the blood stream and subsequent multiplication of the virulent colony types. Infection with virulent colony types appears to be primarily bacteremic in this model. Preliminary experiments indicated that chicken embryos may be protected against the lethal infection by prior treatment of the inoculum with normal and immune rabbit serum. This protective effect was not associated with bactericidal activity. The chicken embryo model is potentially useful as a means of investigating attributes of virulence of gonococci and factors in immunity against gonorrhea.