Peptidoglycan (PG), a heteropolysaccharide component of the mycobacterial cell wall can be shed during
tuberculosis infection with immunomodulatory consequences. As such, changes in PG structure are expected to have important implications on
disease progression and host responses during
infection with Mycobacterium tuberculosis. Mycobacterial
amidases have important roles in remodeling of PG during cell division and are implicated in susceptibility to
antibiotics. However, their role in modulating host immunity remains unknown. We assessed the bacterial burden and host immune responses to M.
tuberculosis mutants defective for either one of two PG N-acetylmuramyl-
L-alanine amidases, Ami1 and Ami4, in bone marrow-derived macrophages (BMDM) and C57BL/6 mice. In infected BMDM, the single deletion of both genes resulted in increased proinflammatory
cytokine responses. In mice,
infection with the Δami1 mutant led to differential induction of pro-inflammatory
cytokines and
chemokines, decreased cellular recruitment and reduced lung pathology during the acute phase of the
infection. While increased proinflammatory
cytokines production was observed in BMDM infected with the Δami4 mutant, these effects did not prevail in mice.
Infection using the Δami1 and Δami4 Mtb mutants showed that these genes are dispensable for intracellular mycobacterial growth in macrophages and mycobacterial burden in mice. These findings suggest that both Ami1 and Ami4 in M.
tuberculosis are not essential for mycobacterial growth within the host. In summary, we show that
amidases are important for modulating host immunity during Mtb
infection in murine macrophages and mice.