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Mycobacterium avium ssp. paratuberculosis (MAP) is the causative agent of Johne's disease (JD), a chronic inflammatory bowel disease of cattle characterized by intermittent to chronic diarrhea. In addition, MAP has been isolated from Crohn's disease (CD) patients. The impact of MAP on severity of clinical symptoms in JD as well as its role in CD are yet unknown. We have previously shown that MAP is able to colonize inflamed enteric tissue and to exacerbate the inflammatory tissue response (Suwandi et al., 2014). In the present study, we analyzed how repeated MAP administration influences the course of dextran sulfate sodium (DSS)-induced colitis. In comparison to mice exposed to DSS or MAP only, repeated exposure of DSS-treated mice to MAP (DSS/MAP) revealed a significantly enhanced clinical score, reduction of colon length as well as severe CD4 + T cell infiltration into the colonic lamina propria . Functional analysis identified a critical role of CD4 + T cells in the MAP-induced disease exacerbation. Additionally, altered immune responses were observed when closely related mycobacteria species such as M. avium ssp. avium and M. avium ssp. hominissuis were administered. These data reveal the specific ability of MAP to aggravate intestinal inflammation and clinical symptoms. Overall, this phenotype is compatible with similar disease promoting capabilites of MAP in JD and CD.

Mycobacterium avium subspecies paratuberculosis (MAP) causes Johne's disease, a chronic granulomatous enteritis in ruminants. Furthermore, infections of humans with MAP have been reported and a possible association with Crohn's disease and diabetes type I is currently discussed. MAP owns large sequence polymorphisms (LSPs) that were exclusively found in this mycobacteria species. The relevance of these LSPs in the pathobiology of MAP is still unclear. The mptD gene (MAP3733c) of MAP belongs to a small group of functionally uncharacterized genes, which are not present in any other sequenced mycobacteria species. mptD is part of a predicted operon (mptABCDEF), encoding a putative ATP binding cassette-transporter, located on the MAP-specific LSP14. In the present study, we generated an mptD knockout strain (MAPΔmptD) by specialized transduction. In order to investigate the potential role of mptD in the host, we performed infection experiments with macrophages. By this, we observed a significantly reduced cell number of MAPΔmptD early after infection, indicating that the mutant was hampered with respect to adaptation to the early macrophage environment. This important role of mptD was supported in mouse infection experiments where MAPΔmptD was significantly attenuated after peritoneal challenge. Metabolic profiling was performed to determine the cause for the reduced virulence and identified profound metabolic disorders especially in the lipid metabolism of MAPΔmptD. Overall our data revealed the mptD gene to be an important factor for the metabolic adaptation of MAP required for persistence in the host.