Spirillae are a bacterial – genus of the family Spirillaceae. They were discovered in 1832 by the naturalist Christian G. Ehrenberg.
What are spirillae?
The genus Spirillaceae formerly included five species and was controversial, as only the species Spirillum volutans and Spirillum winogradskyi could be shown to be related. The three species Spirillum minus, Spirillum pleomorphum and Spirillum pulli have been assigned to the genus from morphological observations. A direct species relationship could not be proven by DNA- composition. Therefore, the deficient and makeshift classification has recently been extended by additional generic categories. The genus Spirillum now contains the 2 species Spirillum volutans and Spirillum pleomorphum. The other species have been classified into further genera like Aquaspirillum. In addition, new Spirillum species such as Aquaspirillum serpens are discovered and older ones are renamed. In contrast to members of the original spirilla genus, salt-loving spirillas have now been discovered and placed in the Oceanospirillum genus. For nitrogen-fixing spirillas, the genera Azospirillum and Herbaspirillum were created. Spirillum minus, which causes rat-bite fever, has not yet been clearly assigned.
Occurrence, distribution and characteristics
Since the re-categorization was done only recently and a description of all species of the new spirillum genera is beyond the scope, the following section refers to the germs originally classified under spirillums. Spirillae are gram-negative bacteria. Thus, only a thin murein layer with a lipid membrane as cell envelope is present. The rigid helical shape is striking and gives the bacteria their name. For locomotion, spirillae use polytrich- bipolar flagellation, i.e. flagellation at both ends of the spiral-shaped cell. Spirillae are relatively large, with a diameter of 1.4-1.7 µm and a length of 14-60 µm. The respiratory metabolism of the bacterium is specialized on organic substrates. A utilization of carbohydrates is not possible. Unlike most aerobic organisms, Spirillum does not possess a catalase. Catalase is an enzyme responsible for the cleavage of hydrogen peroxide. Spirillums are therefore very sensitive to hydrogen peroxide. Due to the poor degradation of hydrogen peroxide, spirillae have microaerophilic properties and therefore prefer low-oxygen environments. An environment with approximately 20% of the oxygen present in normal air provides a good living condition for the bacterium. Spirillum cannot survive in an environment without oxygen. Spirillum is also sensitive to high concentrations of sodium chloride. A concentration of 0.2 g/L NaCl can already have a killing effect. Spirillums are found especially in freshwater due to their Nacl intolerance. Since the germ is also microaerophilic, it survives particularly well in freshwater with low oxygen content. However, various species of spirilla can also be found in other liquids. In fresh pig slurry, for example, the species Spirillum volutans can be detected in a very high concentration. Despite the microaerophilic preference of spirillae, it is also possible to cultivate them in the laboratory at normal oxygen concentrations. Special culture media are required for efficient cultivation, since carbohydrates cannot be utilized as energy by the spirillae.
Diseases and ailments
The species Spirillum minus can cause rat-bite fever in humans. Rat bite fever is an infectious disease that occurs primarily in Japan. The route of transmission of the disease is called zoonosis. This describes transmission from animals to humans. The infection can be caused by bites from rats and other rodents. Other vectors can be pets that eat rodents, such as dogs or cats. Rat bite fever is very rarely transmitted worldwide and only plays a major role in Japan. There it is referred to as “sodoku.” Incubation of the disease can last up to three weeks. Subsequently, skin lesions begin to appear on the wound. A red exanthema forms and the sufferer suffers from episodes of fever that may last for several days and subside periodically every 4-5 days. The disease can last from weeks to months.Convalescence takes place over a similarly long period of time. It is also possible for the sufferer to recover without medical assistance. However, some Japanese experts warn of serious consequences and give a death rate of 5-10% for patients who try to cure rat-bite fever without medical assistance. Lymphangitis may occur as an accompanying symptom. Lymphangitis is a very rare inflammation of the lymphatics. The most obvious symptom of lymphangitis is painful red streaks that appear under the skin on the lymphatic channels. The lymphatics in the subcutaneous fat tissue (subcutis) are particularly affected. In rat bite fever, the typical streaks originate from the red exanthema of the infected wound. The lymph nodes near the site of inflammation then enlarge and serve as a lymph drainage area. Colloquially, lymphangitis is also called “blood poisoning”. This term is misleading, however, because lymphangitis does not occur in the blood and cannot be compared symptomatically with sepsis, i.e. actual blood poisoning. However, lymphangitis can be the precursor of true sepsis in very rare and severe cases of rat bite fever. For this to occur, however, the infection must become severe enough to spread to the bloodstream.
