Latent Viral Infection of Cells in Tissue Culture. VIII. Morphological Observations of Psittacosis Virus in L Cells. ∗

Summary

With the 6BC strain of psittacosis virus only 10% of L cells could be infected in vitro in several culture media, even with repeated exposure to virus over a period of 8 hours at 37°C or 24 hours at 4°C. However, all cells became susceptible to infection during a period of 96 hours at 37°C, suggesting a sequential change in susceptibility. Using the balanced salt solution of Earle or a synthetic medium deficient in phenylalanine, the virus infected the cells and entered a latent phase as well as it did with a complex horse serum-lactalbumin hydrolysate-yeast extract medium, but virus growth did not occur until the missing amino acid or acids were supplied. No structures characteristic of virus were visible in these cells during the phase of latent infection when examined with the light or electron microscope.† Histochemical studies of the growth of virus in L cells revealed that the virus inclusion body contained RNA and DNA.