Growth of Mycobacterium bovis, Bacille Calmette-Guerin, within human monocytes-macrophages cultured in serum-free medium

Mycobacterium bovis BCG is an opportunistic agent that may be responsible f or disseminated disease in immunocompromised individuals. Under physiologic al conditions, macrophages are the natural hosts and final killers of BCG. In the context of inherited or acquired immune disorders underlying dissemi nated BCG infections, macrophages fail to eradicate BCG or even to restrict its intracellular growth. The direct contribution of macrophages, in this setting of impaired BCG destruction, probably depends on the type of underl ying immune deficiency and remains to be experimentally investigated. As an initial approach, we document here the fate of BCG within human monocytes and human monocyte-derived macrophages (MDMs) cultured in commercially avai lable serum-free medium (M-SFM). This medium was used to avoid potential pr oblems associated with human or animal serum-supplemented medium. We show h ere that both monocytes and MDMs cultured in M-SFM display the morphologica l features and functional activities expected for such cells. We also show that after an initial phase of intracellular destruction, BCG grow within i nfected monocytes-macrophages, as shown by colony forming unit (CFU) counts and Ziehl-Nielsen staining. By an electron microscopic analysis, we show t hat the BCG always reside within phagosomes and that 24-h postinfection man y phagosomes stain for the hydrolytic enzyme acid phosphatase. Finally, we compare bacterial growth in vitro within phagocytes from healthy individual s and patients with chronic granulomatous disease (CGD), an inheritable con dition associated with disseminated BCG infection in vivo. No destruction o f intracellular BCG was achieved by the patients cells, revealing the essen tial mycobactericidal role of the respiratory burst in human phagocytes. In vestigations of BCG growth within MDM cultured in M-SFM from patients with other conditions which predispose to clinical BCG infection is therefore wa rranted. (C) 1999 Elsevier Science B.V. All rights reserved.