Ultrastructural differentiation of the genogroups in the genus Ehrlichia

Abstract

Ultrastructural characteristics of 15 strains and isolates of ehrlichiae belonging to three genogroups, or clades of genetically related organisms united in the genera Ehrlichia, Cowdria, Anaplasma, Neorickettsia and a strain of Wolbachia pipientis which represents a fourth genogroup in this cluster of species, were studied in continuous cell culture or in vivo: E. canis (Oklahoma strain and VHE isolate), E. muris (AS 145), E. chaffeensis (Arkansas, 91HE17 and Sapulpa), human granulocytic ehrlichiae (HGE)(BDS, 96HE27, 96HE37, #54, #55 and #72), E. equi (MRK), E. sennetsu (Miyayama), E. risticii (HRC-IL). Wolbachia pipientis was studied in the naturally infected Aedes albopictus mosquito cell line Aa23. All organisms were similar in the normal ultrastructure of individual cells and in the ability to form abnormal, pathological ehrlichial cells of the same type irrespective of the species. Normally all ehrlichiae studied in cell culture existed in two morphological forms -reticulate and dense-cored cells, both of which could divide by binary fission. Most alterations were related to their membranes, especially the cell wall. Differences in the structure of intravacuolar microcolonies (morulae) of ehrlichiae and their inter-relations with the host cells allowed differentiation of the genogroups: the E. canis-E. chaffeensis-E. muris genogroup formed large morulae, with many ehrlichiae, often suspended in a fibrillar matrix, and the host cell mitochondria and endoplasmic reticulum usually aggregated near the morulae and were in contact with the morula membrane; the E. phagocytophila-E. equi-HGE group morulae had no fibrillar matrix, no contacts with host cell mitochodria, and they did not aggregate around the morulae; E. sennetsu-E. risticii group usually developed in small individual vacuoles that did not fuse with each other and divided along with the ehrlichiae.

ankA : an Ehrlichia phagocytophila Group Gene Encoding a Cytoplasmic Protein Antigen with Ankyrin Repeats

“…HL-60 cells were infected with HGE agent and propagated in vitro until at least 50% of them contained ehrlichial morulae as determined by Romanowsky staining. At that point, approximately 2.5 ϫ 10 6 HL-60 cells were prepared for immunoelectron microscopy, as previously described (22,23). Ultrathin sections were reacted with a monoclonal antibody directed against AnkA {IE3; immunoglobulin G1 kappa chain [IgG1()]} and with a control antibody.…”

Granulocytic ehrlichiosis: an emerging or rediscovered tick-borne disease?

“…It appears that there is inhibition of phagolysosome fusion (unpublished observations); thus the bacteria may not be exposed to lysosomal enzymes and may also evade the neutrophil's oxidative burst. Similar changes and inclusions have been described for E. equi and HGE infections [40]. The bacteria are released from neutrophils by unknown mechanisms, but they may be found in the plasma of infected sheep, which is in turn infective [47].…”

“…E, equi and the HGE agent have both been grown in the human promyelocytic leukaemia cell line HL60 [39], where both form similar intravacuolar microcolonies (morulae) that differ greatly from those formed by ehrlichiae of other genogroups [40]. E. equi has been cultured in a tick-cell line [41].…”

Tropical and exotic infections

“…E. sennetsu was first described in Japan in 1955 [115] as a cause of infectious mononucleosis. It falls into genogroup III and like E. risticii, the cause of Potomac fever in horses, its cell division inside parasitophorous vacuoles stimulates expansion and division of the vacuole itself [116]. Sennetsu fever is believed to be transmitted by ingestion of raw fish and sporadic cases are reported from Japan and Malaysia.…”