Growth and lethal effects of the psittacosis agent in chicken embryos of different ages.

Stewart, Robert B. (University of Rochester, Rochester, N. Y.). Growth and lethal effects of the psittacosis agent in chicken embryos of different ages. J. Bacteriol. 83:423-428. 1962.-Inoculation of the psittacosis agent (strain 6BC) into the yolk sacs of chicken eggs in different stages of embryonic development resulted in a steady decrease in ld(50) titer as the embryos increased in age from 7 to 10 days. Correlated with the decreased ld(50) titers in older eggs was the finding that the titers of the organism were lower in the yolk-sac tissues of the older eggs. The embryos themselves also gained appreciably in resistance with increase in age, since comparable titers of psittacosis organisms were found in embryonic tissues of differing ages at the time of inoculation but the mortality of older embryos was considerably less. This resistance of older embryos to the lethal effects of the psittacosis agent could not be demonstrated when the organism was introduced intravenously instead of into the yolk sac.