Propagation and Growth Cycle of Rickettsia quintana in a New Liquid Medium

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The growth cycle of Rickettsia quintana was studied for the first time in liquid culture. Growth of the microorganism in a transparent broth medium was made possible by the finding that fetal calf serum (FCS), but not calf serum (CS), satisfied the requirement of R. quintana (Fuller strain) for red blood cell lysate. The three constituents of the medium, other than FCS, were autoclavable. The growth cycle was characterized by a lag phase of approximately 24 hr, an exponential growth phase of 72 hr, and a doubling time of approximately 4.5 hr. In FCS medium, titers increased 105-fold over starting titers and reached a peak after 5 days of greater than 108 colony-forming-units (CFU)/ml. Optical density readings at 520 nm (OD520) served as useful estimates of the titers only during the last 30 hr of exponential growth. Before this time, titers were below 3 × 107 CFU/ml and could not be detected at OD520. The growth-promoting activity of FCS appeared to be a normal serum component widely distributed among fetal calves. FCS from five commercial suppliers supported growth of R. quintana. The active factor(s) was: (i) non-dialyzable, (ii) resistant to heating at 56 C for 30 min, and (iii) partially inactivated at 100 C in 2 min and completely lost at 100 C in 10 min. The results emphasize the presence of erythrocyte and serum factors other than hemoglobin which stimulate the growth of R. quintana.

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