The organelle needed to digest bacteria would be a lysosome. Lysosomes are found in most cells, but are particularly plentiful in macrophages, because these cells engulf and destroy bacteria and other pathogens.Lysosomes are small membranous sacs of enzymes. There are about forty different hydrolytic enzymes that have been identified in the lysosomes of cells.
Once a macrophage engulfs a bacteria by the process of phagocytosis, the bacteria ends up in a membranous sac called a phagosome. When a phgosome encounters a lysosome inside the cell, the two membranes fuse. This creates a phagolysosome, which is where the bacteria get digested. So in answer to your question, an active macrophage would probably have an abundance of both lysosomes and phagolysosomes present.
khoob - I am assuming that you meant which organelle must be plentiful in macrophages. If that is the case, to digest invading bacteria, the organelle must contain enzymes that will breakdown the bacteria. Lyzosomes are organelles that contain hydrolytic enzymes that will digest macromolecules.
The lysozome can also digest old organelles, viruses and food particles in addition to digesting bacteria.