Evaluation of the chick embryo for the determination of relative virulence of Neisseria meningitidis

The chick embryo model was evaluated as a method to compare virulence between selected strains of Neisseria meningitidis. Inoculation of 13‐day‐chick embryos via the egg yolk distinguished strains having an LD50 of 103 colony forming units (CFU) or greater (low virulence) from those having an LD50 of approximately 101 or less (high virulence). A strain of serogroup B and a spontaneous nonpiliated strain of group C were found to be of relatively high virulence while a strain of N. lactamica, a serogroup A carrier strain, and certain nongroupable strains were found to be of low virulence. Strains having an LD50 of 102 were not differentiated from either of these. Alternatively, inoculation of the chorioallantoic membrane (CAM) of 9‐day‐old chick embryos statistically differentiated most strains of N. meningitidis although inoculation via this route was less sensitive.