Figure 2. Strain-distinctive intracellular niche preferences are also retained in vivo.

Groups of eight mice each were infected through the aerosol route with the individual Mtb strains (100–150 bacilli/lung¹³). At 15 days later these mice were sacrificed and the lungs harvested. Lungs from two mice in each group were taken for TEM imaging and panels (A,B) shows the representative micrographs obtained. Panel (A) shows two representative images of lung cells containing phagosome-enclosed bacteria for the H37Rv (marked by black box) where phagosomal membranes (marked by red arrows) surrounding the bacteria can be distinguished from the bacterial cell wall (marked by yellow arrows). Lower image shows the blown up Mtb structure, boxed (black) in the upper low power shot showing the lung field. Magnification–1 um. 70–100 cells were observed in lung sections for all lung investigations. Panel B confirms cytosolic residence of JAL2287 and MYC431 bacteria in the lung cell field (marked by black box). Upper panels represent low power images showing the lung macrophages followed by their respective high power shots in the lower panels. Continuity of the bacterial wall (black arrows) of the Mtb (Black box) from the low power is shown in the images. Magnification–500 nm and 1 um (upper) and lower–200 nm in both cases. Panel (C-(i)) and (C-(ii)) show the blown up images showing distinct absence and presence of vesicle structure in lung macrophages, for the indicated strains respectively. Yellow arrows mark the bacterial wall, whereas, the vesicle membrane is marked by red arrows. Field from left side images of both panels (marked by boxes-red and black) are blown up to show the Mtb structures in the adjacent panels Magnification: 500 nm. Lysates were generated from lungs of the remaining six mice per group, and plated for determination of the Cfu values (D). Values are the mean ± S.D.