THE ARITHMETIC LINEAR GROWTH OF MYCOBACTERIUM TUBERCULOSIS VAR. HOMINIS

Abstract

The existence of a logarithmic growth phase is accepted as being a fundamental characteristic of bacterial growth. A growth phase wherein the increase in bacterial mass is linear with time ("linear growth") has been observed previously as a rare occurrence and under unusual conditions. In this study, such growth (termed "arithmetic linear growth") was consistently observed as a growth phase of the H37Rv strain of M. tuberculosis var. hominis in a modified liquid Dubos medium. Growth was measured turbidimetrically both with the highly sensitive Coleman model 7 photonephelometer and the Coleman junior spectrophotometer. The arithmetic linear growth phase was of about 12 days duration and followed directly after the logarithmic phase. This phenomenon was also observed with other mycobacteria in other media. It is proposed that linear growth is a consequence of some as yet undefined change in the culture medium.