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L-form bacteria – Definition, Size and shape, Culturing , Applications

L-form bacteria Definition

“L-form” bacteria are also referred to as L-phase bacteria or L-phase variants, and cell wall deficient (CWD) bacteria are bacteria with no cell walls. They were first identified around 1935, by the scientist Emmy Klieneberger Nobel who identified them as “L-forms” after the Lister Institute in London which she was working at.

Two kinds of L-forms can be distinct: unstable L-forms spheroplasts which are capable of splitting however they are able to revert back to the original morphology and stable L-forms forms that are not able to change back to their original bacteria.

Some bacteria that are parasites like mycoplasma have a cell wall as well however they cannot be classified as L-forms since they’re not originated from bacteria that typically contain cell walls.

So far, researchers have discovered more than 50 bacteria species capable of changing into the L-form, and it is possible that more species will be discovered in the near future. “Probably most bacterial species can be converted into L-forms if treated with the antibiotics that inhibit cell wall synthesis,” claims the researcher Josep Casadesus. 1)

Certain kinds of bacteria known as L-form which are implicated in chronic diseases include Bacillus anthracis, Treponema pallidum, Mycobacterium tuberculosis Helicobacter Pylori, Rickettsia prowazekii and Borrelia Burgdorferi. Some species are not able to cause disease.

L-form bacteria replicate in many ways, such as budding, filamentous growth, and binary fission. Certain species of L-forms like Proteus may create large bodies that reproduce through division. In other cases there are granules that bud out from the organism’s body and create small colonies of the L-form.

The L-form bacteria, however, have been able to effectively infect and live within the immune system’s cells that are designed to kill bacteria. Once inside these cells they are no longer identified in the system of immune defense, and can remain in the body for long durations of time. L-form bacteria can affect many types of cells , but prefer to attack macrophages, which are white blood cells.

Size and shape

L-form bacteria are pleomorphic. which means they are able to alter in size and shape. For the most part of their lives they are small, around 0.01 millimeters in diameter.

Because they are smaller than fungal or viruses particles, they are not examined using a normal optical microscope. The smaller, distinct forms of bacteria that are L-form are usually known as coccoid body. Coccoid organisms can be found in groups and appear to be pearls strung together

Sometimes, bacteria that are L-form are able to break free from the cells. In the laboratory, they may expand into thick, thin biofilm filaments that are 60-70 microns in size. Biofilm filaments consist of L-form bacteria, as well as the protective protein sheath. There are many reasons why L-forms also can develop into huge “giant” bodies.

The L-form bacteria do not have flagella which are long, slender appendages that allow certain kinds of bacteria to move forward with whip-like movements. Instead, they glide towards their final destinations in a snail-like manner.

The L-form group of bacteria is usually enclosed within tubules. They are also kept from the surrounding environment within the cell by an exoskeleton or membrane which prevents the bacteria from getting digested by cells.

Culturing of L-form bacteria

Types of bacteria that have cell walls can be developed outside of within the organism (grown inside the lab). But L-form bacteria face a lot of difficulties surviving in a foreign environment. To be able to reproduce effectively in the lab conditions have to be comparable to the conditions found within the body (grown in living conditions). They can therefore be grown in a blood agar, which is grown at extremely certain temperatures and with the pH of a specific.

The notion that certain bacteria are not able to be grown in vitro isn’t new. Researchers have known for a long time they could not. Neither (Syphilis Treponema pallidum ) nor leprosy (Mycobacterium leprae) can be easily grown in the outside of the body.

L-form bacteria employ a variety of measures to ensure that they live throughout the length of time they can within a cell. They can infect all kinds of cells, including white ones however, they seem to prefer to attack macrophages, which is the kind of white blood cell that, at 45 days, have the longest duration of life.

A variety of studies have proven that when they are inside macrophages L-form bacteria can be able to slow Apoptosis also known as programmed cell death permitting them to live within the cell for an extended period of time that’s more that 45 days.

Detection of L-form bacteria

PCR testing

Classical bacterial species can be identified by an in-lab test known as”Polymerase Chain Reaction (PCR). PCR is a method of identifying and amplifying the DNA and proteins of bacteria which have been eliminated. Since L-form bacteria can persist within macrophages for long durations, only a few of them will die, and only a small amount of L-form bacterial proteins as well as genetic material are able to enter bloodstreams at any time, a quantity so tiny so that PCR test is unable to identify them.

Even if small fragments from L-forms which were killed are discovered through PCR tests, the remaining fragments typically are not of the bacterial species that are causing the greatest injury on the patients. This is due to the fact that the most well-adapted and persistent bacteria are those which have the most efficient strategies for survival and are therefore less likely to die.

Antibody testing

L-forms are also not found in antibody tests. Antibodies are Y-shaped proteins which are present in blood. They are utilized by your immune system in order to detect and neutralize foreign substances, including bacteria.

The antibodies form when bacteria have already died. Because L-form bacteria can to remain for lengthy periods within cells, only a few antibodies are made due to their presence.

Appearance of L-form bacteria 

The morphology of bacteria is determined by the cell’s wall. Since the L-form lacks a cell wall it has a morphology that is different from the morphology of the bacteria strain that it was derived from. The typical L-form cells are spheroids or spheres. For instance, L-forms of the rod-shaped bacteria Bacillus subtilis appear to be round when observed using the phase contrast microscope or Transmission electron microscope.

While L-forms can be derived from Gram-positive and from Gram-negative bacteria the test for Gram stain, the L-forms will always be colored Gram-negative because of the absence of the cell wall.

Cell division of L-form bacteria

Cell walls are essential for cell division. This, in the majority of bacteria, happens via binary fission. The process generally involves a cell wall and elements of the bacterial cytoskeleton like FtsZ. The capacity of bacteria that are L-form to divide and grow without the presence of either of these structures is quite unique, and could represent a type in cell division which was essential in the early stages of life. This new method of division is believed to be based on the expansion of tiny protrusions off the cell’s surface. These protrusions subsequently pinching off to create new cells. The absence of a cells’ walls in L-forms implies that division is disordered and results in various cell sizes that range from tiny to extremely large.

Types of L-form bacteria 

L-forms can be differentiated into four types: 

  1. Unstable spheroplast L-forms
  2. Stable spheroplast L-forms
  3. Unstable protoplast L-forms
  4. Stable protoplast L-forms.

Cells that belong to spheroplast-type forms contain a certain cell wall structure, whereas protoplast-type cells are devoid of any cell wall structure. That is, cells are not walled. Protoplasts can be defined as cells that lack a wall structure as viewed by ultrathin sections as well as electron microscopy.


Unstable L-forms are able to revert into normal-walled parents. Bacteria (N-form) are able to induce agents like penicillin are removed. They are thought to be genetically similar to the N-form however they could be deficient in some capacity such as the capability for being attacked by bacteria known as bacteriophages.


Stable protoplast-type spheroplasts and sphero are not able to return to the N-form of their parents. They must be regarded as genetically different from the parent strains as stable mutants that exhibit drastic pleotropic differences in their traits. The changes involve an altered colony as well as cell morphology, inability to create cells with intact walls capsules, flagella, capsules and pili. They also show changes in the lipid and protein elements of the cytoplasmic Membrane (CM) as well as the diminution in or lack of proteolytic extracellular activity resistance to bacteriophages, B-lactam antibiotics, and none or minimal toxic and harmful effects on laboratory animals.

Significance and applications Of L-Forms

The importance of L-forms could be observed in four different areas:

  • as research tools that enable to gain a better understanding of functional and structural organization of bacterial cells.
  • A unique expression system that can be used in biotechnology and medicine.
  • As pathogenic, commensal, and symbiotic species that are associated with mammals, including humans. They can also be utilized for treatment of diseases and
  • Artificially linked organisms that are cultivated with plants, they give them new characteristics, like resistance to diseases.


  • Allan EJ, Hoischen C, Gumpert J. Bacterial L-forms. Adv Appl Microbiol. 2009;68:1-39. doi: 10.1016/S0065-2164(09)01201-5. PMID: 19426852.
  • L-form bacteria, chronic diseases and the origins of life, Jeff Errington, Katarzyna Mickiewicz, Yoshikazu Kawai and Ling Juan Wu, Published:05 November 2016
  • Errington, J. (2013). L-form bacteria, cell walls and the origins of life. Open Biology, 3(1), 120143–120143. doi:10.1098/rsob.120143 

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Why do Laboratory incubators need CO2? What is Karyotyping? What are the scope of Microbiology? What is DNA Library? What is Simple Staining? What is Negative Staining? What is Western Blot? What are Transgenic Plants? Breakthrough Discovery: Crystal Cells in Fruit Flies Key to Oxygen Transport What is Northern Blotting?
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