Early history. Robert Koch’s discovery and laboratory culture of the causative agent of tuberculosis (Mycobacterium tuberculosis), was announced in 1882, and by the end of the century many other varieties of mycobacteria had been described in animals, birds, and also in the environment as non-disease causing organisms.
The earliest report of growth of mycobacteria other than M. tuberculosis – so called nontuberculous mycobacteria (NTM) – dates back to the late 1880s when Alvarez and Tavil described the organism later known as Mycobacterium smegmatis. The first probable description of MAC came with the finding of “tuberculosis” in chickens (avian) that mimicked disease seen in humans, described in England in 1868. By 1890, it was recognized that this avian bacteria (now known as Mycobacterium avium) was distinct in the laboratory from the human variety of M. tuberculosis. Human disease due to MAC was not recognized until almost a half century later. In 1933, human-derived disease causing (pathogenic) strains were reported. Later studies revealed the organisms to be M. avium complex. In 1943, one of the first human cases of MAC was described when a mycobacterial species later identified as Mycobacterium avium was recovered from the sputum of a patient suffering from chronic lung disease with an associated underlying lung illness called silicosis (related to silica inhalation). By 1953 (10 years later), more cases of M. avium like organisms in humans were described by other investigators along with four cases that later were identified as M. intracellulare. At that time, these and other scientists thought that these organisms probably had little or no ability to cause disease (virulence) and that these strains were actually avian tubercle organisms that had lost their ability to cause disease in chickens.