Parachlamydia acanthamoebaEnters and Multiplies within Human Macrophages and Induces Their Apoptosis

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Abstract
Parachlamydia acanthamoebais an obligately intracellular bacterium that naturally infects free-living amoebae. It is a potential human pathogen and may survive in human macrophages. We studiedP. acanthamoebaentry into, and multiplication within, human monocyte-derived macrophages. After 8 h of incubation, 80% of macrophages were infected with a mean of 3.8P. acanthamoebaorganisms per cell. Electron microscopy demonstrated that parachlamydiae were in an intracellular vacuole. After infection with living organisms, the number of parachlamydiae per macrophage increased 4 times from day 0 to day 4, whereas heat-inactivated parachlamydiae were eliminated during the same period. Quantitative PCR confirmed thatP. acanthamoebareplicates within macrophages. Transcriptional activity ofP. acanthamoebawas detected by reverse transcription-PCR targeting the gene encoding ADP-ATP translocase (tlc).P. acanthamoebaexerted a cytopathic effect on macrophages. When macrophages were infected with living bacteria, their number decreased significantly from day 0 to day 4 due to apoptosis, as shown by annexin-V binding and electron microscopy. This study shows thatP. acanthamoebaenters and multiplies within human macrophages before inducing their apoptosis.

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