Fusobacteria: friends or enemies?

, medical expert
Last reviewed: 24.06.2018

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According to the classification accepted in microbiology, fusobacteria belong to prokaryotes and are gram-negative anaerobic bacteria that inhabit the human body and other mammals, being part of a permanent normal microbiocenosis or microflora. Their family - Fusobacteriaceae - has more than a dozen species.

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Morphology of fusobacteria and features of their metabolism

The structure of fusobacteria is unicellular, in the form of a rod similar to spindle (in Latin fusus) - because of the sharp points on both sides. The rods can be thick and thin, straight and curved, and a threadlike shape can also occur. The length of these bacteria varies from 0.0005 to 0.008 mm, there are no organs of movement, although in some sources it is claimed that they have peritricchial (located on the entire surface) flagella.

Bacteriologists note that these microorganisms do not form a dispute, that is, in the case of deteriorating conditions of life, they can not turn into cells with a dense shell. Reproduction of fusobacteria occurs by mitotic cleavage of one cell into two with horizontal transfer of genes concentrated in the nucleoid.

The morphology of fusobacteria partly determines the habitats of their colonies: the mucous membranes of the mouth, respiratory tract, urogenital area and the lower part of the digestive tract - the large intestine. In the blood, their presence is not established, yes it is fusobacteria and to no avail, because the nutrients they receive by the oil fermentation of glucose, sucrose, maltose and some amino acids.

So in the basis of the metabolism of these microorganisms is the biochemical process of anaerobic (without oxygen) dissimilation of carbohydrates under the influence of enzymes. Metabolites are low molecular weight butane acid, carbon dioxide and hydrogen. To get the energy of the bacteria, hydrogen is needed, and its ions take the surface protein fuzobaktery Adhesin A (FadA), and then moves them inside the cell.

By the way, butyric acid is very important for maintaining intestinal homeostasis (absorption of water and electrolytes) and for the regeneration of cells of the mucosal epithelium; physicians have established a relationship between the lack of this acid in the intestine and the development of local inflammatory pathologies (for example, ulcerative colitis). In addition to fusobacteria, oleic acid is produced by bacteria of the genus Clostridium.

On the conditional pathogenicity of fusobacteria

Fusobacteria, like most gram-negative anaerobes, are considered bacteriologically opportunistic, but there are strains in which scientists no longer doubt the increased pathogenicity. In particular, it is found in the oral cavity and intestines of Fusobacterium necrophorum, as well as Fusobacterium nucleatum, which has chosen dental plaque for habitation.

How does their pathogenic mechanism work? The outer surface of the cytoplasmic membrane of fusobacteria consists of polymerized fats, proteins and carbohydrates in the form of lipopolysaccharides, which are bacterial toxic substances (endotoxins) and, simultaneously, antigens. That is, these compounds cause an immune response of the body and an inflammatory response without an obvious exogenous (external) effect on individual systems and organs.

There is an opinion that the pathogenicity of some bacteria of the family Fusobacteriaceae is manifested only in case of weakening of immunity, however, it should be taken into account that they have been shown to have the ability to increase aggressiveness, since fusobacteria produce phospholipase A, an enzyme that breaks down the lipids of cell membranes and opens up access of bacteria to the cells of all tissues. But "single-handedly" this enzyme microorganisms, as a rule, do not use, but in the presence of pathogenic microorganisms activity is significantly increased. In case of damage to the mucous streptococcus or Staphylococcus fusobacterium, taking advantage of the case, penetrate deeper and cause necrotic inflammation of the tissues. The most illustrative example of such synergistic action is gangrenous pharyngitis (or Simanovsky-Plaut-Vincent's angina), which arises from infection of the mucous membrane with gram-negative bacteria Spirochaetales Borrelia vincentii, Prevotella intermedia and Fusobacterium nucleatum.

What diseases cause fusobacteria?

And now we list some diseases caused by fusobacteria, more precisely, pathologies that develop with their more than active participation. To them doctors include:

  • pulpitis of carious teeth;
  • gingivitis;
  • periodontal disease;
  • osteomyelitis of the jaw;
  • phlegmon of different localization;
  • tonsillitis and paratonzillitis (phlegmonous tonsillitis);
  • chronic form of sinusitis;
  • ophthalmic abscess after streptococcal angina with necrosis and sepsis (Lemierre syndrome);
  • bronchiectatic disease;
  • purulent pneumonia;
  • abscess of the lungs;
  • empyema of the pleura;
  • abscesses of the brain;
  • suppurative inflammation of abdominal organs;
  • erosive balanitis and balanoposthitis;
  • acute colpitis (vaginitis) and vulvitis;
  • purulent-septic complications of medical abortions;
  • ulcerative colitis;
  • Crohn's disease;
  • septicemia.

Researchers at the Harvard Medical School and the Dana-Faber Cancer Institute conducted a genomic analysis of tumors in colorectal cancer and found in them an abnormally large number of Fusobacteria F. Nucleatum. To date, studies are continuing to confirm (or refute) the hypothesis put forward about the involvement of fusobacteria in the development of cancer of the colon and rectum. The fact is that the surface protein of bacteria, adhesin A (which we mentioned above), binds to the transmembrane glycoprotein of human epithelial cells with E-cadherin. This protein provides intercellular adhesion in our tissues and can "glue" cancer cells, preventing their invasion. But fusobacteria neutralize it, resulting in unimpeded proliferation of cancer cells.

Treatment of fusobacteria

The treatment of fusobacteria, or rather, drug therapy fusobacteriosis is carried out with antibiotics.

Among antibacterial drugs, doctors prefer the most active against F. Nucleatum and F. Necrophorum: clindamycin, carbenicillin, cefoxitin, cefoperazone, cefamandol, phosphimycin, ornidazole. The purpose of a particular medication, of course, depends on the diagnosis and clinical picture of the disease.

Carbenicillin (trade names - Karbetsin, Fugacillin, Microcillin, Piocyanil, etc.) acts only on gram-negative bacteria and is used in cases of peritonitis, septicemia, meningitis, osteomyelitis as part of complex therapy.

Second-generation cephalosporin antibiotic Cefoxytin (Mefoxin, Atralxitin, Boncefin) is recommended for a wide range of bacterial aetiology, including tonsillitis, pneumonia, urinary tract infections, bones, joints, skin, soft tissue; is assigned to prevent infectious complications after operations.

A preparation of Fosfomycin (Fosfomycin trometamol, Monural, Urophosfabol) is used for urological bacteriosis - recurrent cystitis or nonspecific urethritis (once 3 g).

At the beginning of the article, we promised to find out the degree of danger to a person of a tiny unicellular fusobacterium. Yes, it can be pathogenic, but, on the other hand, a person can not get rid of her presence in the microflora.

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