What is the significance of finding a wild type strain (that doesn't usually replicate) to replicate in weakened macrophages?
Wild strains are more virulent than the laboratory ones. They are the standards of genotype, compared with strains that have been modified in the laboratory. Wild strains mutate because they need to adapt to the environment. Their discovery enables us to find the organisms resistant to antibiotics, antibodies etc. This allows the development of new vaccines to combat these organisms (macrophages synthesis of specific antibodies for the secondary immunity).