Growth Physiology of Mycobacteria in Modified Dubos Liquid Medium

Abstract

Although mycobacteria grow in Dubos liquid medium showing an arithmetic linear growth, the initial few days of growth were found to correspond to an 'induction' period. In this period, rapid increase of the amount of growth occurred, whereas increase of the number of colony-forming units remained at a low level. This finding shows that the rapid increase of the amount of growth is accompanied by rapid death of multiplied bacteria. In a successive period, which was considered to correspond to the logarithmic growth phase, a 1:1 correspondence existed between the amount of growth and the number of colony-forming units. The induction period is not considered to be a lag phase, in which the bacteria grow slowly, but a period of unbalanced relationship between the growth and the viability. Even when we inoculated different sizes of bacteria, the amounts of growth became similar in both inoculations after several days of incubation. However, the number of colony-forming units remained always smaller in the use of small inocula than in the use of large inocula. In the use of small inocula, much more rapid increase of the amount of growth occurred. However, this rapid increase gave rise to rapid death of bacteria.