GROWTH OF RICKETTSIA PROWAZEKI IN IRRADIATED MONOLAYER CULTURES OF CHICK EMBRYO ENTODERMAL CELLS

Abstract

The growth of Rickettsia prowazeki (Madrid E strain) in unirradiated and irradiated cultures of chick embryo entodermal cells was investigated. Monolayer entodermal cell cultures were prepared on glass without plasma from explants of a vascular membranes of 4-day-old chick embryos. Three days after explanation the cultures were exposed to 10,000 to 300,000 r of Co60 gamma-radiations. The smallest dose which produced widespread morphological changes was 60,000 r. The cells disappeared from the glass or lost affinity for dyes at higher exposures in the following percentages: 60% with 100,000 r in 7 days, 90 to 95% with 200,000 r in 7 days, 99 to 100% with 300,000 r in 4 days. The nutrients of irradiated and control cultures were replaced, 8 to 18 hrs after the beginning of irradiation, with nutrients containing high concentrations of partially purified rickettsiae. The growth of the microorganisms was followed for 7 days by examination of stained cultures and titration of fluids in eggs. Infection of the cultures required relatively high concentrations of rickettsiae, but a moderate amount of growth was obtained in unirradiated cultures. Cell cultures that had received 10,000 to 100,000 r supported the growth of rickettsiae to approximately the same extent as unirradiated controls. With doses of 150,000, 200,000, and 300,000 r greater numbers of rickettsiae were released into the nutrients, during the first few days of infection, than in control cultures. Rickettsial titers became lower than those of the controls, however, when almost all the entodermal cells had disappeared from the glass. The results suggest that irradiation did not enhance rickettsial multiplication, but simply elicited a more rapid release of the microorganisms during the period in which the host cells lysed.