Infection of Acanthamoeba polyphaga with Simkania negevensis and S-negevensis survival within amoebal cysts

Simkania negevensis, a novel microorganism belonging to the family Simkania ceae in the order Chlamydiales, has an intracellular developmental cycle du ring which two morphological entities, elementary bodies (EB) and reticulat e bodies (RB), are seen by electron microscopy. Rates of seropositivity to the organism are high in certain population groups, and S. negevensis has b een associated with respiratory illness in humans. This study reports for t he first time the ability of S. negevensis to survive and grow inside Acant hamoeba polyphaga in addition to its known ability to grow in cell cultures of human or simian origin. Infectivity of S. negevensis and growth in amoe bae were monitored by immunoperoxidase assays. Long-term persistence and ex ponential growth of S. negevensis in amoebal trophozoites were demonstrated by infectivity assays and by electron microscopy. EB and dividing RB of S. negevensis were observed within inclusion bodies inside A. polyphaga. When S. negevensis-infected A. polyphaga amoebae were exposed to adverse condit ions resulting in encystation of the amoebae, several possible outcomes wer e observed: cysts containing both normal amoebic cytoplasm and S. negevensi s; cysts in which S. negevensis cells were relegated to the space between c yst walls; and cysts containing S. negevensis, but apparently lacking amoeb al cytoplasm. S. negevensis within dried amoebal cysts was capable of long- term survival. The possibility that amoebae may have a role in natural tran smission of S. negevensis needs to be investigated.