Growth of Mycobacterium lepraemurinum in the mouse bone marrow: an ultrastructural study

The ultrastruct of the mouse bone marrow during the first 8 weeks after intravenous inoculation of animals with 10(9) Mycobacterium lepraemurium is described. The bacteria were almost exclusively in macrophages, which became converted to epithelioid cells after 8 weeks, at which time they were very heavily infected. The nature of the exceptionally rapid increase in numbers of bacteria in the bone marrow compared with other tissues early in the infection is discussed. It is concluded that a short doubling time of bacteria situated in the marrow is a more probable explanation than recruitment from elsewhere in the animal.