Four distinct families of Gram-negative, extremely thin and long, helical bacteria that can move actively establish the group of spirochetes. They occur in soils and waters and as parasites or commensals in the digestive tracts of mammals, mollusks, and insects. Several species appear in humans as causative agents of spirochetes, including such diverse diseases as Lyme disease, leptospirosis, and treponematosis.
What are spirochetes?
Spirochetes embody a group of Gram-negative bacteria characterized by a very thin and corkscrew-like coiled (helical), flexible, long cell body. Their diameter reaches only 0.1 to 3.0 micrometers, while their length can be up to 250 micrometers in some species. Spirillae, for example, a group of bacteria that are also helical, are distinguished from spirochetes by their external flagella and by their rigid cell body, whereas that of spirochetes is flexible and pliable. Their small diameter allows them to easily pass through bacterial filters. Spirochetes can actively move with a unique locomotor system. It consists of bundled filamentous proteins (fibrils) and axially arranged filaments, also known as endoflagellae or internal flagellae, because they are located inside the cell body. Endoflagella allow them to actively move in a meandering or twisting motion. With the help of the fibrils and endoflagella, the bacteria can also move in a jerky manner. Part of the filaments consists of tubulin-like scaffolding proteins, which are rarely found in bacteria. The environment in which spirochetes can thrive varies widely. Strictly anaerobic spirochetes can be distinguished from facultatively anaerobic and aerobic spirochetes. Microaerophilic species also exist, which find growth conditions only at oxygen concentrations far below normal atmospheric oxygen levels.
Occurrence, distribution, and characteristics
Spirochetes form a very heterogeneous group within bacteria. Some authors argue for assigning a separate class to the spirochetes, of which only four different families are known. Corresponding to the very heterogeneous metabolism of the spirochetes is also their distribution and occurrence. Spirochetes are widely distributed as free-living bacteria in soils, waters and aquatic mud. These are species that have no health relevance to humans. Other species of spirochetes colonize the digestive tracts of mollusks, insects, and other arthropods. The rectal sections of wood-feeding insects such as termites are particularly heavily populated with spirochetes. It is possible that the bacteria play a role in the degradation of lignin in wood-eating insects. Various species of spirochetes can also be detected throughout the digestive tracts of mammals and humans. Spirochetes even form part of the oral flora in mammals and humans. They are even present in the rumen of ruminants. In the vast majority of cases, spirochetes occur as commensals or parasites. This means that they predominantly exert a neutral to slightly parasitic effect in the digestive tract. A possible, direct health benefit for humans has not yet been demonstrated. However, a few species of spirochetes from each of the four families are highly pathogenic. They are causative agents of mild to severe diseases that can be transmitted by insect bites, tick bites, or by direct introduction of the pathogens through minute skin lesions or through contact with mucous membranes. In most cases, the pathogens can be readily controlled with antibiotics during the initial stages of the diseases.
Diseases and symptoms
Widely known, for example, is Lyme disease, which is transmitted almost exclusively by infected ticks. The disease is caused by Borrelia burgdorferi bacteria, which belong to the spirochetes, and takes very different courses that can cause problems even after years. The lymphatic system and cranial nerves are frequently affected. For example, unilateral or bilateral facial paresis or myocarditis may occur as a result of the infection. Other species of Borrelia are known to cause the s. The venereal disease syphilis, also called hard chancre or French disease, is caused by Treponema bacteria, which also belong to the group of spirochetes.The disease is transmitted almost exclusively during sexual intercourse through contact with the sites of inflammation on the external genital organs. Treponema pertenue, a Treponema bacterium that also belongs to the spirochetes, is the causative agent of another treponematosis called framboesia. This non-venereal infectious disease of the tropics initially manifests as itchy and weeping raspberry-like papules on the lower legs – and often on the face in children. If left untreated, the disease leads to serious changes in bones and joints in the third stage, which sometimes breaks out only after a rest period of 5 to 10 years. Infection usually occurs through insect bites, but the bacteria can also enter the body through direct skin contact with papules, via minute lesions of the skin. The disease can be treated well with antibiotics in the early stages. One of the four families of spirochetes is formed by leptospires, some species of which are also pathogenic to humans. They are the causative agents of so-called leptospiroses. Of several known leptospiroses, only Weil’s disease shows a severe course if untreated. Leptospiroses are known by names such as rice fever, swine guardian disease, or sugarcane fever. The names indicate that close contact with animals poses a risk of infection. Infected mammals such as rats, mice, dogs, and hedgehogs, as well as pigs and cattle, excrete leptobacteria into the environment through their urine, which enters the body through minute lesions of the skin or through the mucous membranes. Leptospirosis has become very rare in Germany thanks to observed hygiene and the availability of effective antibiotics.
