ELECTRON MICROSCOPIC OBSERVATIONS OF THE DEVELOPMENT OFCOXIELLA BURNETIIIN THE CHICK YOLK SAC

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Abstract
Yolk sac material, obtained daily over a period of 1 week from embryos inoculated with seed of phase-I C. burnetii strain Ohio-314 containing 250 units of penicillin, was examined by electron microscopy and other technics for the presence of rickettsiae. The concentration of rickettsiae in the yolk sac, as determined by electron microscopy, light microscopy, the complement-fixation test, recovery of organisms and mouse infectivity was low for the first 3 days, increased rapidly 3 to 5 days after infection and then remained relatively constant. Rickettsiae in 3- to 7-day cultures, when observed by electron microscopy, had dense fibrillar centers surrounded by less-dense cytoplasmic material containing granules approximately 15 m[mu] in diameter. The whole was enclosed by multiple external layers. Many appeared to be in various stages of binary fission, and one form which contained a cross-wall was observed. These forms readily combined with ferritin-labeled specific antibody. In rare instances, several kinds of "atypical" forms which did not combine with ferritin-labeled antibody were found in the cytoplasm of yolk-sac cells 4 to 5 days after inoculation; it is not certain whether these forms are artifacts or normal stages in the maturation of C. burnetii. These atypical forms were not observed in subsequent experiments in which embryonated eggs were inoculated with doses of penicillin varying from 0 to 4,000 units per egg.