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 LD( 50) of 10(3) colony forming units (CFU) or greater (low virulence) fro m those having an LD(50) of approximately 10(1) or less (high virulenc e). A strain of serogroup B and a spontaneous nonpiliated strain of gr oup C were found to be of relatively high virulence while a strain of N. lactamica, a serogroup A carrier strain, and certain nongroupable s trains were found to be of low virulence. Strains having an LD(50) of 10(2) were not differentiated from either of these. Alternatively, ino culation of the chorioallantoic membrane (CAM) of 9-day-old chick embr yos statistically differentiated most strains of N. meningitidis altho ugh inoculation via this route was less sensitive.