Figure 4. Representative transmission electron micrographs (TEM) depict Acanthamoeba castellanii amebae during A) 10-minute, B) 30-minute, and C) 24-hour co-cultures (multiplicity of infection 100) with Yersinia pestis (CO92 pgm+, pCD1, pGFPuv, amp+). Red arrows in panel A indicate potential intraameba mitotic division of Y. pestis bacterium. Visual analysis of TEM micrographs proved inconclusive for identifying the bacterial division septum. Y. pestis resides within the potential replicative niche of a tight-fitting vacuolar membrane, similar to Yersinia-containing vacuoles observed in macrophages. YP, Y. pestis; CV, central vacuole; DV, digestive vacuole; M, mitochondria. Scale bars indicate 3 μm.