Abstract
Johne's disease is a chronic granulomatous enteritis of ruminants caused by the intracellular bacterium Mycobacterium avium subsp. paratuberculosis (Map). We previously demonstrated that Map isolates from sheep persisted within host macrophages in lower CFUs than cattle isolates after 7 days of infection. In the current study, we hypothesize that these phenotypic differences between Map isolates may be driven be the fatty acids (FAs) present on the phosphadidyl-1-myo-inositol mannosides of the Map cell wall that mediate recognition by the mannose receptors of host macrophages. FAs modifications may influence Map's envelope fluidity ultimately affecting pathogenicity. To test this hypothesis, we investigated the responses of two Map isolates from cattle (K10 isolate) and sheep (2349/06-1) to the bovine and ovine macrophage environment by measuring the FAs content of extracellular and intracellular bacteria. For this purpose, macrophages cell lines of bovine (BOMAC) and ovine (MOCL-4) origin were infected with the two isolates of Map for 4 days at 37°C. The relative FAs composition of the two isolates recovered from infected BOMAC and MOCL-4 cells was determined by gas chromatography and compared with that of extracellular bacteria and that of bacteria grown in Middlebrook 7H9 medium. Using this approach, we demonstrated that the FAs composition of extracellular and 7H9-grown bacteria was highly conserved within each Map isolate, and statistically different from that of intracellular bacteria. Analysis of FAs composition from extracellular bacteria enabled the distinction of the two Map strains based on the presence of the tuberculostearic acid (18:0 10Me) exclusively in the K10 strain of Map. In addition, significant differences in the content of Palmitic acid and cis-7 Palmitoleic acid between both isolates harvested from the extracellular environment were observed. Once the infection established itself in BOMAC and MOCL-4 cells, the FAs profiles of both Map isolates appeared conserved. Our results suggest that the FAs composition of Map might influence its recognition by macrophages and influence the survival of the bacillus within host macrophages.
Highlights
Mycobacterium avium subsp. paratuberculosis (Map) is the etiological agent of Johne’s disease (JD) or paratuberculosis, a chronic granulomatous enteritis of ruminants
Much of what is known of the roles of phophatidyl1-myo-inositol mannosides (PIMs) in Mycobacteriahost interaction is derived from in vitro studies using various cell models and purified PIMs molecules or whole mycobacterial cells (Guerin et al, 2010; Torrelles and Schlesinger, 2010)
In Mycobacterium tuberculosis (Mtb), the nature of its fatty acids (FAs) has been shown to impact the spatial conformation of the PIMs mannose caps for recognition by the mannose receptor (MR), the host immune response and the fate of the bacillus within human macrophages (Torrelles et al, 2008)
Summary
Mycobacterium avium subsp. paratuberculosis (Map) is the etiological agent of Johne’s disease (JD) or paratuberculosis, a chronic granulomatous enteritis of ruminants. Macrophages primarily use the mannose receptor (MR, CD207) as well as the complement 3 receptor for the phagocytosis of Map (Souza et al, 2007) These receptors are distinguished by the fact that they mediate the engulfment of microbes without necessarily inciting a proinflammatory immune response and thereby have long been postulated to enhance early intracellular survival of some microbes. Continued efforts to define the factors affecting the early interaction between Map and host macrophages are necessary to further our understanding of the pathogenesis of paratuberculosis and final disease outcome. This ongoing research might help in the development of better control strategies and diagnostic techniques
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