L-forms of bacteria (synonym for L-variants of bacteria). The ability to transform into L-forms, or L-transformation, is inherent in all types of bacteria. Currently L-forms are also obtained from Treponema pallidum. Regardless of the species of bacteria, L-forms are formed by actions that block some parts of the cell wall biosynthesis, and at the same time inhibit the division of a bacterial cell while maintaining its growth. The ability to L-transformation depends on the origin of cultures, the degree of their sensitivity to the transforming effect, the individual characteristics of the strains and individual cells of the population.
The formation of L-forms may be in the nature of a direct primary reaction to the effect of a transforming agent or be the final phase of changes that at the time of initial contact with a transforming agent manifest as forms of heteromorphic growth or subcellular forms like spheroplasts. L-transformation is completed by the formation of characteristic L-colonies, which are divided into two types - "ZV" and "FOR".
Colonies "ZV" - the size of 0.5-2 mm, mucous consistency, with a lace edge, tightly growing into the environment, pigmented center. They consist of spherical bodies of different sizes and optical density, filamentous and vacuolised forms containing inclusions in the form of granules; in their composition there are also loose granules forming the center of the colony. L-elements of the colonies "STAR" retain the cell wall (albeit in a modified form) and antigenic bonds with bacteria of the original species.Go
The colonies “FOR” are significantly smaller (up to 0.5 mm), with a dry consistency, whitish with a delicate lace edge and a dense center firmly bonded to the medium. They also contain spherical and vacuolised bodies of different sizes and compositions with inclusions in the form of submicroscopic granules. Their composition is dominated by submicroscopic structures that form the central part of the colony, there are many structures of uncertain, all-time changing configuration. The origin of these structures is associated with the emergence of cellular content due to increased permeability or destruction of bacterial walls.
L-elements of the colonies “FOR” are for the most part deprived of the cell walls and partly lose the antigenic composition of the original bacterial forms. The morphology of the colonies and the microscopic structural elements of L-colonies is so characteristic that it can be considered a typical trait differentiating the L-forms of bacteria from other forms of bacterial variability. The formation of L-colonies of the type “ST” and “FOR” is noted in almost all known species of bacteria.
L-forms of bacteria can multiply in a variety of ways: by dividing, budding and decay into the smallest elementary bodies that have the ability to reproduce. Despite the physical and osmotic fragility of L-elements, they are very viable and can last for a long time without reseeding in the culture medium. They are highly resistant to L-transforming agents. The ability of bacteria to persist for a long time and to be interchanged in the L-form, regardless of the content in the medium of the L-transforming agent, is called stabilization. It is due to hereditary fixation of L-signs. Recovery from L-fb. cells of the original bacteria are called reversion. It depends on the degree of stabilization of the L-fb population, the number of preliminary passages on the medium with the transforming agent, and the cultivation conditions. Reversion is reproduced experimentally with the exclusion of a transforming agent from the medium or its destruction.Go
In terms of ability to reversion, each population of L-forms is heterogeneous, since individual individuals of the population have a different ability to reversion. Therefore, even in highly stable cultures, individuals can be found (although rarely) that retain the ability to reversion. Morphological manifestations of reversion are diverse. At the same time, the formation of various forms of incomplete division, sometimes morphologically similar to the initial phases of L-transformation, segmented or budding bacilli sticks, usually unusual for this type of morphology, is observed. Depending on the degree of stabilization of the L-forms, the reversion process is accompanied by a more or less pronounced restoration of the characteristics of the original species. Revertants of L-forms are characterized by an increased ability to L-transformation, due to the peculiar state of their cell wall, which reacts to effects that are unable to cause the formation of L-forms in bacteria that have not previously undergone L-transformation.
Among the L-forms of pathogenic bacterial species, there may be strains that retain the original virulence degree characteristic of the parent culture (for example, finds of virulent L-forms of Vibrio cholerae, toxigenic strains of L-forms of Clostridium tetani, etc.). Practically avirulent strains of stable L-forms are also far from indifferent to a macroorganism, since they persist for a long time in it, have a dermotoxic effect and, when administered repeatedly, cause an increased reaction, resulting in the occurrence of severe, non-healing sterile abscesses and the death of animals. L-forms of some pathogenic species of bacteria have a selective cytopathic effect on a number of tissue cultures (see). L-forms are often found in the body with such long-term pathological processes as brucellosis, septic endocarditis, rheumatism, etc. These data indicate the possible role of L-fb. in infectious pathology.