| Summary: | <p>Abstract</p> <p>Background</p> <p>Chlamydiae induce persistent infections, which have been associated with a wide range of chronic diseases in humans and animals. Mixed infections with <it>Chlamydia </it>and porcine epidemic diarrhea virus (PEDV) may result in generation of persistent chlamydial infections. To test this hypothesis, an <it>in vitro </it>model of dual infection with cell culture-adapted PEDV and <it>Chlamydia abortus </it>or <it>Chlamydia pecorum </it>in Vero cells was established.</p> <p>Results</p> <p>Infected cultures were investigated by immunofluorescence (IF), transmission electron microscopy (TEM) and re-infection experiments. By IF, <it>Chlamydia</it>-infected cells showed normal inclusions after 39 hpi. Dual infections with <it>Chlamydia abortus </it>revealed a heterogenous mix of inclusion types including small inclusions consisting of aberrant bodies (ABs), medium-sized inclusions consisting of ABs and reticulate bodies and normal inclusions. Only aberrant inclusions were observable in dual infection experiments with <it>Chlamydia pecorum </it>and PEDV. TEM examinations of mixed infections with <it>Chlamydia abortus </it>and <it>Chlamydia pecorum </it>revealed aberrant chlamydial inclusions containing reticulate-like, pleomorphic ABs, which were up to 2 μm in diameter. No re-differentiation into elementary bodies (EBs) was detected. In re-infection experiments, co-infected cells produced fewer EBs than monoinfected cells.</p> <p>Conclusions</p> <p>In the present study we confirm that PEDV co-infection alters the developmental cycle of member species of the family <it>Chlamydiaceae</it>, in a similar manner to other well-described persistence induction methods. Interestingly, this effect appears to be partially species-specific as <it>Chlamydia pecorum </it>appears more sensitive to PEDV co-infection than <it>Chlamydia abortus</it>, as evidenced by TEM and IF observations of a homogenous population of aberrant inclusions in PEDV - <it>Chlamydia pecorum </it>co-infections.</p>
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