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

Setting: The interaction of tubercle bacilli with macrophages is central to understanding of tuberculosis disease.

Objective: The objective was to determine whether prior passage within macrophages affects the behavior of Mycobacterium tuberculosis (Mtb) upon re-entry into other macrophages.

Design: Transmission electron microscopy was used to monitor fusion of bacterial phagosomes with late endosomal/lysosomal compartments using thoria as a fluid phase marker. Two-dimensional polyacrylamide gel electrophoresis was used to study bacterial protein expression within macrophages.

Results: H37Rv and BCG expressed novel proteins within macrophages. H37Rv also underwent less fusion after intracellular (IC) (24.2±7.7%) than extracellular (XC) (67.4±5.5%) passage when the bacteria entered new macrophages in small clusters. These effects were inhibited by serum, and were not observed with H37Ra or BCG bacteria (78.9±1.6% fused for all conditions). In addition, vacuoles which contained single bacilli were less likely to acquire markers (26.9±2.6%) than those that contained multiple bacilli (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 express proteins within macrophages that alter their interaction with these host cells.