Clostridium is a genus of anaerobic, Gram-positive bacteria. Species of Clostridium inhabit soils and the intestinal tracts of animals, including humans.[1] This genus includes several significant human pathogens, including the causative agents of botulism and tetanus. It also formerly included an important cause of diarrhea, Clostridioides difficile, which was reclassified into the Clostridioides genus in 2016.[2]
History
In the late 1700s, Germany experienced several outbreaks of an illness connected to eating specific sausages. In 1817, the German neurologist Justinus Kerner detected rod-shaped cells in his investigations into this so-called sausage poisoning. In 1897, the Belgian biology professor Emile van Ermengem published his finding of an endospore-forming organism he isolated from spoiled ham. Biologists classified van Ermengem's discovery along with other known gram-positive spore formers in the genus Bacillus. This classification presented problems, however, because the isolate grew only in anaerobic conditions, but Bacillus grew well in oxygen.[1]
Circa 1880, in the course of studying fermentation and butyric acid synthesis, a scientist surnamed Prazmowski first assigned a binomial name to Clostridium butyricum.[3] The mechanisms of anaerobic respiration were still not yet well elucidated at that time, so taxonomy of anaerobes was still developing.[3]
In 1924, Ida A. Bengtson separated van Ermengem's microorganisms from the Bacillus group and assigned them to the genus Clostridium. By Bengtson's classification scheme, Clostridium contained all of the anaerobic endospore-forming rod-shaped bacteria, except the genus Desulfotomaculum.[1]
As of October 2022, there are 164 validly published species in Clostridium.[4]
The genus, as traditionally defined, contains many organisms not closely related to its type species. The issue was originally illustrated in full detail by a rRNA phylogeny from Collins 1994, which split the traditional genus (now corresponding to a large slice of Clostridia) into twenty clusters, with cluster I containing the type species Clostridium butyricum and its close relatives.[5] Over the years, this has resulted in many new genera being split out, with the ultimate goal of constraining Clostridium to cluster I.[6]
"Clostridium" cluster XIVa (now Lachnospiraceae)[7] and "Clostridium" cluster IV (now Ruminococcaceae)[7] efficiently ferment plant polysaccharide composing dietary fiber,[8] making them important and abundant taxa in the rumen and the human large intestine.[9] As mentioned before, these clusters are not part of current Clostridium,[5][10] and use of these terms should be avoided due to ambiguous or inconsistent usage.[7]
Biochemistry
Species of Clostridium are obligate anaerobe and capable of producing endospores. They generally stain gram-positive, but as well as Bacillus, are often described as Gram-variable, because they show an increasing number of gram-negative cells as the culture ages.[11]
The normal, reproducing cells of Clostridium, called the vegetative form, are rod-shaped, which gives them their name, from the Greek κλωστήρ or spindle. Clostridium endospores have a distinct bowling pin or bottle shape, distinguishing them from other bacterial endospores, which are usually ovoid in shape.[citation needed] The Schaeffer–Fulton stain (0.5% malachite green in water) can be used to distinguish endospores of Bacillus and Clostridium from other microorganisms.[12]
There is a commercially available polymerase chain reaction (PCR) test kit (Bactotype) for the detection of C. perfringens and other pathogenic bacteria.[13]
Biology and pathogenesis
Clostridium species are readily found inhabiting soils and intestinal tracts. Clostridium species are also a normal inhabitant of the healthy lower reproductive tract of females.[14]
The main species responsible for disease in humans are:[15]
The vegetative cells of clostridia are heat-labile and are killed by short heating at temperatures above 72–75 °C (162–167 °F). The thermal destruction of Clostridium spores requires higher temperatures (above 121.1 °C (250.0 °F), for example in an autoclave) and longer cooking times (20 min, with a few exceptional cases of more than 50 min recorded in the literature). Clostridia and Bacilli are quite radiation-resistant, requiring doses of about 30 kGy, which is a serious obstacle to the development of shelf-stable irradiated foods for general use in the retail market.[22] The addition of lysozyme, nitrate, nitrite and propionic acid salts inhibits clostridia in various foods.[23][24][25]
Clostridium botulinum produces a potentially lethal neurotoxin used in a diluted form in the drug Botox, which is carefully injected to nerves in the face, which prevents the movement of the expressive muscles of the forehead, to delay the wrinkling effect of aging. It is also used to treat spasmodic torticollis and provides relief for around 12 to 16 weeks.[27]
Nonpathogenic strains of Clostridium may help in the treatment of diseases such as cancer. Research shows that Clostridium can selectively target cancer cells. Some strains can enter and replicate within solid tumors. Clostridium could, therefore, be used to deliver therapeutic proteins to tumours. This use of Clostridium has been demonstrated in a variety of preclinical models.[31]
^ abNewman, Sir George (1904). Bacteriology and the Public Health. Philadelphia, Pennsylvania: P. Blakiston's Son and Co. pp. 107–108. ISBN9781345750270.
