Studies on cell-wall deficient non-acid fast variants of Mycobacterium tuberculosis

While the host-parasite relationship in tuberculosis still remains incompletely understood, there has been recent renewed interest in indications that tubercle bacilli are converted into metabolically inactive, non-acid fast (NAF) granular forms in the presence of host defence mechanisms and antituberculosis drugs. The present study investigates the mechanism of induction of these NAF variants in vitro and in vivo, and their ultimate pathogenicity. Evidence is provided that appears to clearly indicate that acid-fast mycobacteria are converted into NAF, cell wall deficient variants which remain dormant, only to revert to the parent, acid-fast bacilli in immune-compromised hosts, thence ultimately producing disease. It is then suggested that this may be one of the causes of the observed persistence of the bacilli in hosts in spite of chemotherapy. In a typical study in experimental animals in the present investigation, NAF variants were separated from lung lavage by differential centrifuging. When these were then injected into animals made immune-deficient with Freund's adjuvant or cyclophosphamide, they reverted to parent acid-fast forms. The presence of these NAF forms as variants of M. tuberculosis, and not merely contaminants, was clearly established by a number of methods. These included phase contrast and electron microscopy, immunological studies employing antiserum and comparison with the parent organisms, and gel electrophoresis of the proteins of the parent organisms. Other evidence is also offered confirming the hypothesis of reversion of NAF forms. It is also shown in this study that NAF forms can be induced in vitro by hydrolases.