M: Nutritional studies on Mycobacterium tuberculosis– effect of amino acids on the ‘in vitro’ growth of Mycobacterium tuberculosis

Though tubercle bacilli can grow in a very simple synthetic medium containing salts, inorganic nitrogen and a simple source of carbon, the actual substrates utilized in the tissues of the infected animals are far from clear. The organism is intra-cellular in the early stages of its growth and depend upon the host cell and probably the surrounding medium—the plasma or the lymph for its nutrition. Protein intake has been recognized as a factor in modifying the course of tuberculosis, though its actual mechanism of action is not well denned (Rich, 1951). Since the amino acids are the main sources of synthesis of both the tissue cells and the bacteria, the availability of these amino acids would determine the growth and multiplication of the bacteria. It is also known that certain amino acids reduce the virulence of pathogenic bacteria both ‘in vitro ’ and ‘in vivo ’ (Goodlow et al. 1950; Page et al. 1951) and can function as anti-tubercular agents (Kanazava, 1960). Considering the important role of amino acids at the cellular level, studies have been undertaken to obtain information on (a) the amino acid utilization of M. tuberculosis ‘in vitro’, (b) amino acid changes in the serum of animals during experimental tuberculosis, and (c) the influence of amino acids on the course of the infection. Earlier studies in this field of amino acid metabolism have yielded confusing and contradictory results as can be seen from the following table: TABLE I Effect of amino acids on the growth of M. tuberculosis Utilizable amino acids Non-utilizable amino acids Author Leucine, taurine, asparagin