A. SCHERLER¹, N. JACQUIER¹, G. GREUB<sup>1

1</sup>Institute of Microbiology, University Hospital Center and University of Lausanne, Lausanne, Switzerland

Waddlia chondrophila is an obligate intracellular bacteria belonging to the Chlamydiales order which is associated with abortion in ruminants and miscarriage in humans. Members of the Chlamydiales order are characterized by a biphasic developmental cycle involving adhesion and internalization of elementary bodies, which differentiate into proliferative reticulate bodies. In presence of stress stimuli such as β-lactam antibiotics, interferon-gamma or nutrient starvation, reticulate bodies proliferation is inhibited, inducing the formation of enlarged and persistent aberrant bodies (ABs). The removal of these stress stimuli allows the bacteria to re-enter the normal developmental cycle. From these observations, ABs are thought to play an important role in chronic infections due to Chlamydiales. Nevertheless, the link between chronic infections and presence of ABs has yet to be demonstrated. The aim of this study was to describe W. chondrophila ABs formation, their morphology and potential differences in DNA, RNA and protein content following treatment with different stimuli. ABs morphology, DNA replication and transcription pattern were assessed by immunofluorescence, quantitative PCR and reverse transcription PCR. In this study, we observed two main subtypes of ABs that exhibited different morphologies and number per host cell. Furthermore, we showed that DNA replication of W. chondrophila was differentially affected by the different stimuli. Finally, mRNA expression patterns of important division proteins (MreB and RodZ) could be classified in distinct groups according to the different expression of their encoding genes. These results indicate that distinct subtypes of ABs are induced by the various stimuli, potentially reflecting different mechanisms of ABs formation. Further studies are now needed to increase our knowledge on this persistent stage, and consequently, to improve therapeutic options against chronic chlamydial infections.