Enhancing Action of Egg-Yolk on Virulence of Meningococcus for Mice

Nungester and his coworkers 1 found that gastric mucin of the hog exerts a great enhancing action on the virulence of meningococcus in experimental infection of mice. This observation has been widely confirmed and extended to a number of other microörganisms of low virulence. However, as Miller 2 and Nungester, et al., 3 have pointed out that different lots of mucin varied considerably in their activities and that sterilization by excessive heat might decrease their action, difficulties have been met with in our hands to secure a potent product for experimental work. Recently, in our studies on rickettsiae cultivated in the yolk-sac of the developing chick 4 it was accidentally noticed that rickettsia in yolk was more virulent than the same organisms contained in other tissues. It was thought that possibly yolk has an enhancing action on virulence similar to that of mucin. In order to test this supposition, meningococcus has been chosen for study and the results are herewith communicated.

Materials and Method of Study. Two freshly isolated strains of meningococcus were employed for this study. Both were of low virulence when suspended in saline or Tyrode's solution. Organisms were grown on blood-agar plate for 6 to 16 hours and made up in Tyrode's solution to 500 million organisms per ml as compared with “Wellcome” opacity-tube for the standardization of bacterial vaccines. Decimal dilutions were then made also in Tyrode's solution to obtain decreasing numbers of organisms and were then mixed with 9 volumes of diluted egg-yolk immediately before inoculation.

Fresh egg-yolk was obtained aseptically and emulsified into uniform consistency by shaking vigorously with sterile glass rods. This emulsion was very sticky and its relative viscosity was found to be over 60 as determined with an Oswald's viscosimeter.