Ultrastructural study of Chlamydia pneumoniae in a continuous-infection model.

We have established an in vitro model of long-term continuous Chlamydia pneumoniae infection in HEp-2 cells. Using transmission electron microscopy, we demonstrated the presence of spontaneous abnormal chlamydial inclusions similar in appearance to the persistent chlamydial forms induced in vitro by treatment with cytokines or antibiotics or by nutrient deprivation.

Differential expression of ompA, ompB, pyk, nlpD and Cpn0585 genes between normal and interferon-gamma treated cultures of Chlamydia pneumoniae.

A common feature of many chlamydial infections is that they are often asymptomatic and may persist for long periods of time if left untreated. In addition to the well recognized lytic stage of the chlamydial developmental cycle, evidence is now emerging to support a persistent phase in the cycle in which the reticulate bodies are morphologically abnormal, viable but non-infectious and presumably also have altered gene expression patterns. We used an RT-PCR approach to study the differential levels of gene transcription for 14 genes (16SrRNA, ompA, ompB, omcB, 76 kDa, gseA, pmp1, gltX, hsp60, yaeT, pyk, nlpD, Cpn0585, Cpn1046) between normal and IFN-gamma treated Chlamydia pneumoniae cell cultures. Even though the level of morphologically abnormal reticulate bodies in our IFN-gamma treated cultures was low (approximately 10% morphologically discernible, although presumably a larger percentage were in the persistent state but not yet morphologically altered) we identified five genes (ompA, ompB, pyk, nlpD, Cpn0585) that were clearly upregulated when compared to normal cultures. This gene transcript profile may be characteristic of a general stress state in Chlamydia, induced by IFN-gamma treatment in this case, but perhaps more widely induced in other in vitro and in vivo situations.