Outer membrane channel protein MctB in Mycobacterium tuberculosis is part of a Cu resistance mechanism that ensures low intracellular Cu levels in the bacterium. Human resistance to bacteria, mediated via IFN-gamma-mediated activation of macrophages, may involve the use of reactive Cu(1) in the presence of hydrogen peroxide, since activated Cu is toxic to bacteria. IFN-gamma stimulates the trafficking of the Cu transporter ATP7a to the vesicles that fuse with phagosome and these phagosomes are found to have a high Cu content and an increased bactericidal activity against E.coli. Using MctB, Mycobacterium tuberculosis may limit the amount of excess Cu within it whole in the host [1].

1: Copper resistance is essential for virulence of Mycobacterium tuberculosis. Wolschendorf F, Ackart D, Shrestha TB, Hascall-Dove L, Nolan S, Lamichhane G, Wang Y, Bossmann SH, Basaraba RJ, Niederweis M; Proc Natl Acad Sci U S A. 2011;108:1621-1626. PMID:21205886