The rickettsial agent Coxiella burneti was studied in cultured mouse L cells by use of the electron microscope. Rickettsiae gain entry to the host cell in an apparently passive manner through phagocytic activity by L cells. The L cells show a lysosomal response to the presence of rickettsiae, as determined by cytochemical tests for acid phosphatase and 5′-nucleotidase. Further, examination of C. burneti within lysosomes suggests that rickettsiae can be degraded by the host cell. Autoradiographic analyses using tritiated thymidine show that rickettsial DNA is largely restricted to the dense nucleoid region, and when such labeled rickettsiae are used to inoculate L cells, most of the label becomes localized in the host cell nucleus. The above information is discussed in terms of dynamic interactions between C. burneti and infected L cells.

The nucleoids of the various pleomorphic forms of Chlamydia psittaci have been examined by direct observation of infected cells and by observations on isolated particles. The fixation and staining methods used were the same as those routinely used for the examination of bacteria to facilitate the comparison of chlamydial fine structure with that of bacteria. The nucleoids of reticulate bodies were composed of fine fibrils which extended throughout these particles. The nucleoids of intermediate bodies are characterized by an electron-dense mass with which the fibrous elements are associated in a structurally coherent manner. As condensation of the intermediate bodies proceeds, the electron-dense mass becomes eccentrically located and the fibers form a distinct radiating structure. Large elementary bodies have a few fibers associated with their condensed electron-dense nucleoids but the more condensed mature elementary bodies have a very discrete and homogeneous electron-dense nucleoid which is separated from the cytoplasmic elements of these particles by a very distinct electron-transparent space. These highly condensed elementary body nucleoids are usually ovoid, but may be elongated or irregular, and a small number of these structures react very strongly with ruthenium red. While the nucleoid structure of reticulate bodies resembles that of the bacterial cell, both the condensation process and the nucleoid morphologies which result from it in intermediate and elementary bodies have no parallels among the bacteria. Thus we conclude that major differences in nucleoid organization exist between the chlamydia and the bacteria.

KORDOVA, N., J. C. WILT, and M. SADIQ. 1971. Lysosomes in Lcells infected with Chlamydiapsittaci 6BC strain. Can. J. Microbiol. 17: 955-959. Studies on lysosomal activation of Chlamydia psittaci infected L cells have been performed during the growth cycle of the agent and extended for 4 days after the initiation of infection. The present results Indicate that lysosomes of infected L cells were not injured during phagocytosis, but that lysosomal enzyme release f i s t occurred about 24 h after infection and apparently preceded the death and lysis of host cells. These observations attach a new significance to the study of injury and death of chlamydial infected cultured cells as well as to studies on the pathogenesis of psittacosis at the whole host level.

Coxiella burnetii (Cb) in phase I (Ph I) multiplies very poorly in L-cells as shown by light and electron microscopy and infectivity titrations; Cb antigens, however, are detectable by immunofluorescence in most cells. Phase II (Ph II) organisms, in contrast, multiply well and produce typical particles in well-defined cytoplasmic vacuoles. Density gradient centrifugation has been applied to test the heterogeneity of the animal-maintained Nine Mile strain in Ph I and the corresponding egg-grown strain in Ph II. The evidence indicates that both strains are mixtures of Ph I and Ph II organisms, although they reacted as Ph I or Ph II antigens in the complement fixation test. The interaction of Ph I and Ph II organisms was studied in mixed infections in L-cells; suppression, or a less marked enhancement, of the growth of Coxiella burnetii was observed, depending on the conditions. It is suggested that Ph I and Ph II rickettsiae represent genetically different but closely related organisms, Ph I being the "parent" strain and Ph II the "mutant" strain; "phase variation" of Coxiella burnetii results from a selection of the mutant in the population under the prevailing environmental conditions.

Ko~oovbr, N., L. POFFENROTH, and J. C. WILT. 1972. Lysosomes and the "toxicity" of Rickettsiales. 11. Non-cytocidal interactions of egg-grown C. psittaci 6BC and in vitro rnacrophages. Can. J. Microbiol. 18: 869-873. During the infection of cultured mouse peritoneal phagocytes with egg-grown C. psittaci 6BC strain, lysosomes retained their integrity and host cells were not damaged. Infected monocytes showed greater ability than uninfected monocytes to spread and transform into giant cells containing enlarged nuclei and masses of cytoplasm with clear cytoplasmic vacuoles. Chlamydia1 particles were released from the cytoplasm of infected phagocytes by pseudopodia-like extrusions. These events were in marked contrast to the effect of L cell grown C. psittaci 6BC strain which caused early leakage of lysosomal acid phosphatase into the cytoplasm of macrophages and induced a rapidly progressive irreversible cell damage (14).KORDOVA, N., L. POFFENROTH et J. C. WILT. 1972. Lysosomes and the "toxicity" of Rickettsiales. 11. Non-cytocidal interactions of egg-grown C. psittaci 6BC and in vitro macrophages. Can. J. Microbiol. 18: 869-873. ALI cours de l'infection d'une culture de phagocytes de la cavitC ptritoniale de souris, avec la souche C. psittaci 6BC cultivee dans I'oeuf, les lysosomes ont conservt leur intkgritt et les cellules h6tes n'ont pas CtC endommagees. Les monocytes infectks ont dtrnontrt une plus grande habilete que les monocytes non infectes A se repandre et A se transformer en cellules gkantes, contenant des noyaux plus larges et des masses de cytoplasrne aux vacuoles claires. Des particules chlamydiales ont ttC liberks du cytoplasme des phagocytes infectes par des pseudopodes. Ces observations sont d'un contraste frappant quant a I'effet de la souche C. psittaci 6BC cultivke dans cellules L qui causait la libbation rapide de phosphatase acide du lysosome dans le cytoplasme des lnacrophages et induisait des dommages cellulaires rapidernent progressifs et irrhersibles.