Clostridium

Clostridia (from the Latin generic name Clostridium, from Greek κλωστήρ "spindle") are gram-positive, obligately anaerobic, spore-forming bacteria of the family Clostridiaceae. The endospores are heat resistant and can survive in boiling water for many hours, some at 110 °C for about an hour. Clostridia, with the exception of C. perfringens, can move actively with peritrichous flagella.

The bacteria are so-called environmental germs and occur everywhere (ubiquitously), especially in soils and in the digestive tract (especially as normal flora in the intestine) of higher organisms. They also get into food through dust and soil particles, where they can lead to serious problems (see below).

The genus Clostridia contains pathogenic germs as well as apathogenic species, some of which are used in biotechnology. Among the pathogenic species, Clostridium botulinum (causes botulism), Clostridioides difficile (causes colitis, so-called pseudomembranous colitis) and Clostridium tetani (causes tetanus) are the most important. Other species cause gas gangrene, bradsot, rash gangrene and abomasal pararrhagic gangrene.

From the point of view of their preferred energy source, clostridia can be divided into three major groups:

1. Proteolytic clostridia: cleavage of proteins and/or pairwise conversion of amino acids
2. Uric acid-cleaving clostridia, e.g. C. acidi-urici
3. Saccharolytic clostridia: fermentation of carbohydrates (sugar, cellulose, starch)

The main fermentation products of saccharolytic clostridia are butyric acid, acetone, butanol, carbon dioxide and molecular hydrogen (H2).

Biotechnical significance

Production of organic solvents

Clostridium acetobutylicum is able to ferment sugars to the solvents acetone, 1-butanol, ethanol and to the organic acids acetic acid and butyric acid. The bacterium was used until the middle of the 20th century for the biotic production of the aforementioned organic solvents on an industrial scale. It was first described by the chemist Chaim Weizmann, later the first president of the state of Israel.

In addition, numerous other Clostridia species are used for the biotechnological production of various products or are being researched as potential producers, including Clostridium ljungdahlii, which is useful for synthesis gas fermentation.

Clostridia in agriculture

Clostridia are widely distributed in soils. Saccharolytic clostridia (but not representatives of the other clostridia groups) are able to reduce and thus fix molecular nitrogen (N2). They are therefore called diazotrophs and are natural fertilizer producers in the soil. The most active N2-fixer of the genus is Clostridium pasteurianum in anoxic sediments.

The 10/2005 issue of the dlz agricultural magazine warns against the build-up of clostridia in agricultural biogas plants (co-digestion plants). In such plants, liquid manure from animal husbandry and green waste from municipalities, trade and industry are usually fermented anaerobically at temperatures below 40 °C. Clostridia are found in this process. In this process, clostridia find the best conditions for multiplication. The author recommends ploughing in fermentation substrates and not applying them to green areas. The use of "effective microorganisms" should also reduce the build-up of bacteria.

The NRW Chamber of Agriculture has warned against "scaremongering" with regard to clostridia and biogas slurry. A multiplication of the bacterium Clostridium perfringens, which is often mentioned as problematic, has not been detected so far. In agreement with the Bavarian State Institute for Agriculture, however, a warning is issued against the spreading of carnivore excrement and guano (dry bird excrement), because one hundred thousand times more pathogenic bacteria of the Clostridium perfringens type occur in these than in the excrement of herbivores. Here the bacterial count is 100 - 10000 per 1 ml. The application of fermentation residues from biogas plants to forage crops and pastures could possibly pose a health risk if these products are used.

The risk of botulism, which is caused by Clostridium botulinum, is also to be restricted: In NRW, for example, poultry excrement may only be used on arable land and in biogas plants, but may not be spread on grassland and field grassland.

It seems unlikely that cheese-damaging clostridia can be linked to biogas plants: experience with two farms in NRW over 8 years even shows a particularly low level of contamination.

Medical significance

Food spoiler or poisoner

• C. botulinum - food poisoner
• C. butyricum - food spoilage agent
• C. estertheticum - food spoilage agent, especially chilled meat
• C. pasteurianum - food spoilage agent
• C. perfringens - food poisoner
• C. putrefaciens - food spoiler
• C. sporogenes - food spoilage agent
• C. tyrobutyricum - food spoilage agent, especially in hard cheeses

Clostridium perfringens in particular is known to cause enteritis caused by contaminated food. Clostridium endospores, because of their marked resistance to high temperatures, can survive in the sterilization of canned foods when insufficiently heated. They germinate during storage of the canned food and the clostridia multiply in them, as they do not require oxygen for their metabolism (they are obligate anaerobes). Their metabolism leads to spoilage of the canned food: the canned food is decomposed, unpleasant smelling and tasting acids are formed, the gases formed carbon dioxide (_CO2) and molecular hydrogen (H2) inflate the canned food (so-called bombage). Other foods such as cheese can also be destroyed by gas formation. This is referred to as late bloating. Aseptically packaged beverage cartons containing fruit juice or fruit pulp may also be affected by bombage due to recontamination or if the spore load is high and pasteurization is inadequate.

Medically important Clostridia species

• Clostridium botulinum, causative agent of botulism
• Clostridium chauvoei, causative agent of rinderpest in cattle and sheep
• Clostridioidesdifficile, causative agent of antibiotic-induced intestinal inflammation, pseudomembranous colitis with diarrhea. Enterotoxins and cytotoxins are frequently detectable in patients with the disease.
• Clostridium gigas, causative agent of German Bradsot (also a gas gangrene)
• Clostridium histolyticum, a rare and particularly dangerous gas gangrene pathogen
• Clostridium sordelii, causes gynaecological infections and thus miscarriages and is another rare gaseous pathogen
• Clostridium perfringens, as a causative agent of soft tissue infections the classic gas gangrene pathogen, which also causes food poisoning as well as polymicrobial intra-abdominal infections and peritonitis.
• Clostridium piliforme, causative agent of Tyzzer's disease, which occurs in particular in rodents
• Clostridium septicum, causative agent of gas gangrene in humans and animals and abomasal pararrhagic gangrene of sheep; causing bacteraemia especially in immunosuppressed individuals.
• Clostridium novyi, causative agent of German Bradsot (also a gas gangrene)
• Clostridium tetani, causative agent of tetanus (lockjaw)

Virulence factors

Various virulence factors are present in Clostridia. Clostridium botulinum produces botulinum toxin, which is inactivated after heating at 80 °C for only 30 minutes. The different types hydrolytically cleave proteins that mediate fusion with the synaptic membrane (synaptobrevin, syntaxin, SNAP-25). This in turn inhibits the release of acetylcholine from the synapses. Clostridium tetani produces the tetanus toxin. It is released when the bacterial cell decays. Synaptobrevin is cleaved, and thus the release of the inhibitory neurotransmitters glycine and GABA is inhibited (hence the name tetanus). Clostridium perfringens produces, among other things, toxin alpha (= lecithinase), which destroys cell membranes, and it produces enterotoxins and pore-forming toxins. Clostridioides difficile produces toxins A (enterotoxin effect) and B (cytolytic effect).

The collagenases of the clostridia constitute another virulence factor. With the help of this enzyme, Clostridia can spread particularly rapidly by degrading collagen in the connective tissue of the host organism. Conversely, collagenase from Clostridia is used to support wound healing (debridement).

Treatment

Antibiotics available for the treatment of infections with Clostridium species are penicillin combined with clindamycin or metronidazole, as well as ampicillin, amoxicillin, ampicillin-sulbactam and amoxicillin-clavulanic acid.