Ichiae are coccoid to pleomorphic and vary in size from compact (0.4 ) to big (among 1 and 2 ) (Popov et al., 1995). E. chaffeensis replicates in an intracellular, membrane-bound vacuole derived from host cell membrane, forming microcolonies called morula since they resembling mulberries. Morula is derived from the latin word “morum” for mulberry. Each vacuole contains a single to more than 400 ehrlichiae (Barnewall et al., 1997). E. chaffeensis exhibits tropism for mononuclear phagocytes, and includes a biphasic developmental cycle which requires two morphologically distinct forms, the smaller (0.four.6 ), infectious dense cored cell (DC), and a larger replicating reticulate cell (RC, 0.7-0.9 ). Ehrlichiae possess a gram unfavorable envelope which consist of a cytoplasmic membrane and outer membrane separated by periplasmic space; however, their cell wall lacks peptidoglycan (PG) (2627-69-2 Autophagy Mavromatis et al., 2006). DCs are usually coccoid inshape and characterized by an electron dense nucleoid that occupies the majority of the cytoplasm when RCs are pleomorphic in shape and have uniformly dispersed nucleoid filaments and ribosomes distributed all through the cytoplasm (Zhang et al., 2007). E. chaffeensis has one of many smallest bacterial genome (1.three Mb), encoding up to 1200 proteins, and about half of those genes have predicted or known functions. The genome sequence of Ehrlichia species has revealed low GC content material (30 ), many long tandem repeat sequences (TRs) and one of the smallest genome to coding ratios, that is attributed to lengthy noncoding regions (Dunning Hotopp et al., 2006; Frutos et al., 2006). Presence of extended non coding regions and low GC content material are believed to represent degraded genes inside the final stage of elimination, and enhanced GC to AT mutations found in related Rickettsiales members (Andersson and Andersson, 1999a,b). TRs are actively produced and deleted by way of an unknown mechanism that seems to become compatible with DNA slippage. Generation of TRs in Ehrlichia serves as a mechanism for adaptation towards the hosts, not to produce diversity. Even though TRs share equivalent qualities, there is no phylogenetic relationship between the TRs from diverse species of Ehrlichia, suggesting TRs evolved soon after diversification of each and every species (Frutos et al., 2006). The genome sequence of Ehrlichia has revealed several genes potentially involved in host-pathogen interactions which includes genes coding for tandem and ankyrin-repeat containing proteins, outer membrane proteins, actin polymerization proteins, along with a group of poly(G-C) tract containing proteins, which might be involved in phase variation. Notably, genes encoding proteins related with biosynthesis of peptidoglycan (PG) and lipopolysaccharide (LPS) are absent in the genome. Given that, PG and LPS bind to nucleotide-binding oligomerization domain (Nod)-like receptor proteins and toll-like receptor proteins (TLR4) to activate leukocytes, the absence of LPS and PG presumably helps Ehrlichia to evade the innate immune response elicited by these pathogen-associated molecular patterns (PAMPs). E. chaffeensis consists of two varieties of TRs, modest (12 bp) and huge (10000 bp) period repeats. These TRs may perhaps play function in regulation of gene expression and phase variation (Frutos et al., 2007). Multiple secretion systems have already been described in gram damaging bacteria for the delivery of effector proteins. Within the ehrlichial genome, form I and IV secretion systems happen to be identified (Collins et al., 2005; Dunning Hoto.