Ultrastructural variation of cultured Ehrlichia chaffeensis

Abstract

Summary. The ultrastructure of Ehrlichia chafeensis (Arkansas strain) was studied in nonirradiated and irradiated monolayers of mouse embryo, Vero, BGM and L929 cells, and in non-irradiated DH82 cells. Within the intracellular parasitophorous vacuoles (morulae), two types of ehrlichial cells were found regularly-those with uniformly dispersed nucleoid filaments and ribosomes (reticulate cells) and smaller ones with centrally condensed nucleoid filaments and ribosomes (dense-cored cells), which represent the normal life cycle of ehrlichiae. In addition, large reticulate cells were observed, forming long projections of the cell wall, protrusions 'of cytoplasmic membrane into the periplasmic space, or budding of protoplast fragments (minute forms) into the periplasmic space. Ehrlichiae with abnormalities of protoplast fission were found, apparently leading to formation of giant, multilobular or elongated rod-like ehrlichiae. Morulae were usually surrounded by cisterns of granular endoplasmic reticulum and mitochondria and often contained vesicles, long tubules 25 nm in diameter, probably originating from the ehrlichial cell wall, and fibrillar ehrlichial antigen apparently shed from the surface of the cell wall. Some cells contained, in addition to normal morulae, a whole morula that had become dense and contained degenerating ehrlichiae. These results indicate that as well as normal growth and reproduction, ehrlichiae exhibit pathological events : they can be remarkably damaged inside the host cell vacuoles, presumably phagolysosomes, or enter a process morphologically similar to bacterial L-transformation.

Ultrastructural differentiation of the genogroups in the genus Ehrlichia

“…Unlike what was previously described for E. chaf feensis Arkansas strain [37], mitochondria were not observed adjacent to the morulae. Cisterns of granular endoplasmic reticulum were frequently tightly apposed to the morula membrane along with some cytosolic vesicles (Fig.…”

“…Cell cultures, pellets of neutrophils and small pieces of tissues were fixed in a mixture of formaldehyde 1.25%, glutaraldehyde 2.5% and trinitrophenol 0.03% in 0.05 M cacodylate buffer, pH 7.3 [43], processed further as described earlier [37] until embedding in Poly/Bed 8 12 (Polysciences Inc., Warrington, PA, USA). Some Wolbachia-infected cultures were also fixed at 4°C in glutaraldehyde 2.5% v/v containing CaC12 0.1% w/v and sucrose 1% w/v in 100 mM sodium cacodylate buffer (pH 7.3) and post-fixed in OsO4 1% w/v, stained en bloc with uranyl acetate 2.0% w/v, dehydrated through an ethanol and acetone series, and embedded in an LX-l12/Araldite (Ladd Research Industries, Burlington, VT, USA) mixture.…”

“…Only recently have most of the ehrlichiae been propagated in cell culture systems [24-291, which has permitted more detailed studies of their biology and ultrastructure [5,11,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. Nevertheless, knowledge about the fine structural morphology of the ehrlichiae belonging to the three genogroups remains fragmentary, and no comparison between them has been published.…”

Human Ehrlichioses and Rickettsioses in Cameroon

“…Although they have a characteristic Gram negative cell wall structure, they lack the necessary enzymes to synthesize cell membrane components such as lipopolysaccharide and peptidoglycan (Lin & Rikihisa, 2003). As intracellular pathogens, Ehrlichia reside in cytoplasmic membrane-bound vacuoles inside host cells (granulocytes or monocytes) forming microcolonies called morulae, derived from the Latin word "morus" for mulberry (Popov et al, 1995;Paddock et al, 1997;Ismail et al, 2010). These morulae (ranging in size from 1.0 to 6.0 µm in diameter) may contain 1 to >40 organisms of uniform or mixed cell types (Popov et al, 1995;Rikihisa, 1999).…”

“…As intracellular pathogens, Ehrlichia reside in cytoplasmic membrane-bound vacuoles inside host cells (granulocytes or monocytes) forming microcolonies called morulae, derived from the Latin word "morus" for mulberry (Popov et al, 1995;Paddock et al, 1997;Ismail et al, 2010). These morulae (ranging in size from 1.0 to 6.0 µm in diameter) may contain 1 to >40 organisms of uniform or mixed cell types (Popov et al, 1995;Rikihisa, 1999). Organisms in the family Anaplasmataceae were first described in 1910 when Theiler described Anaplasma marginale, the etiologic agent of an economically important and severe disease of cattle (Mahan, 1995).…”