Intracellular passage within macrophages affects the trafficking of virulent tubercle bacilli upon reinfection of other macrophages in a serum-dependent manner

Objective: The objective was to determine whether prior passage within macr ophages affects the behavior of Mycobacterium tuberculosis (Mtb) upon re-en try into other macrophages. Design: Transmission electron microscopy was used to monitor fusion of bact erial phagosomes with late endosomal/lysosomal compartments using thoria as a fluid phase marker. Two-dimensional polyacrylamide gel electrophoresis w as used to study bacterial protein expression within macrophages. Results: H37Rv and BCG expressed novel proteins within macrophages. H37Rv a lso underwent less fusion after intracellular (IC) (24.2 +/- 7.7%) than ext racellular (XC) (67.4 +/- 5.5%) passage when the bacteria entered new macro phages in small clusters. These effects were inhibited by serum, and were n ot observed with H37Ra or BCG bacteria (78.9 +/- 1.6% fused for all conditi ons). In addition, vacuoles which contained single bacilli were less likely to acquire markers (26.9 +/- 2.6%) than those that contained multiple baci lli (77.3 +/- 2.8%). Conclusion: These results indicate that phagolysosomal fusion patterns can be modulated by a variety of factors and that virulent Mtb bacteria may exp ress proteins within macrophages that alter their interaction with these ho st cells. (C) 2001 Harcourt Publishers Ltd.