Biological properties of dissociative L- and other forms of Mycobacterium bovis

Abstract

A race of modified forms of mycobacteria with special properties that can be promising for the construction of TB vaccines was selected It was found that the persistence of the researched microorganisms (27th subculture of acid-fast bacillus and the L-form) persisted for nine months (the period of research) and longer in the bodies of guinea pigs. However, from the suspension prepared from macroscopically unchanged organs of the experimental animals we found acid-proof elementary bodies (grains) and bacilli of typical morphological forms, which formed an orange culture on the nutrient medium on the third day after suspension seeding. The inoculation of guinea pigs with isolated acid-proof mycobacteria (culture-revertant) (1 mg/cm3) was not accompanied by the development of allergic condition (allergic reaction to the tuberculin and AAM was negative at 30, 60 and 90 days); however, acid-proof bacilli, which formed an orange culture,were isolated on the the third day from experimental animals which had been subjected to euthanasia. Multiple passages through the artificial culture medium (dense), prolonged exposure (20 months) at low plus temperature changed the genetic balance, ensuring their survival as a result of the loss of some (specific to the pathogen) and the acquisition of new properties (especially atypical )which are partly inherent in other mycobacteria. At the same time, the persistence in the body of guinea pigs of typical morphological acid-proof forms (bacilli) that reverse from L-forms was not accompanied by the development of the disease. They are chromogenic and retain the ability to form colonies (culture-revertant) on dense nutrient medium from the first generation (from biological material of the guinea pigs) on the second day of cultivation. The loss of sensitization ability of Mycobacterium bovis which werepassaged many times and persistent in the body of guinea pigs can probably testify to the loss of immunogenic capacity, since the development of allergic (tuberculin) reaction, as well as its intensity, indicates an immunological restructuring of the microorganism (the development of an infection) with the parallel acquisition of the specific resistance. We observed a residual virulence of the researched modified forms of M. bovis with the possible formation of specific antiTB immunity without development of the necessary level, which was the indicator of allergic condition and ulceration of the site where the suspension of mycobacteria was introduced. Microscopy of smears of organs of the euthanized animals (after 80 days)revealled acid-nonproof bacilli, seeding cells. In the control,the weight of the animals tended to increase while the bacterioscopic research (smears) proved negative. Mycobacteria with new, genetically fixed properties have the ability to stimulate benign infectious process, without the development of allergies to the level required for the detection by PPD- for mammals AAM. However, it should be noted that perhaps the extinction of the activity of genes responsible for the pathogenic properties, which are determined by redox processes (dehydrogenase, catalase activity, etc.) and genes which were in a dormant state, activate metabolic processes of pigment synthesis with inhibition of the action of pathogenic factors (toxins). We did not find a relationship between the rate of reproduction (duration of colony formation) and pathogenicity because the original parent culture (third generation) of the investigated modified forms of M. bovis had a high virulence and formed colonies on the second or third day without forming pigment and did not express dehydrogenase and catalase activity. In this article we discuss strains ofM. bovis which differ in biological properties from pathogenic strains.