Figure 2.

Growth characteristics of virulent and attenuated Chlamydia psittaci strains. A, Primary fibroblasts were grown from the peritoneal membrane of DBA2/J mice in 24-well plates and infected with C. psittaci in triplicates with or without interferon gamma (IFN-γ) (10 ng/mL). Infected cells were collected 48 hours after infection and titrated along with the initial inoculum. The burst size (output/input ratio) is compared on a log scale. B, Primary peritoneal macrophages were plated at 5 × 10⁵ cells per well, incubated with or without IFN-γ (10 ng/mL) overnight, then infected at a multiplicity of infection of 1 for 48 hours in triplicates. The burst size is compared on a log scale. C, DBA2/J mice were infected intraperitoneally and euthanized on days 2, 5, and 7 and peritoneal lavage was obtained. The number of C. psittaci in samples was calculated by inclusion-forming unit (IFU) assay. No significant difference in load was observed (n = 3). D, Mice were infected intraperitoneally and killed on day 7, and the number of chlamydiae (IFU) in the peritoneal lavage and the liver was determined. Data are shown as a ratio of chlamydial load in the liver vs the amount in the peritoneal lavage. The ratio was greater for the virulent strain by 2–3-fold but was not statistically significant (n = 3: P = .20).