Clostridium


Clostridium is a genus of Gram-positive bacteria. This genus includes several significant human pathogens, including the causative agents of botulism and tetanus. The genus formerly included an important cause of diarrhea, Clostridioides difficile, which was separated after 16S rRNA analysis. They are obligate anaerobes capable of producing endospores. 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. Clostridium species inhabit soils and the intestinal tract of animals, including humans. Clostridium is a normal inhabitant of the healthy lower reproductive tract of females.
Clostridium cluster XIVa and Clostridium cluster IV efficiently ferment plant polysaccharide composing dietary fiber, making them important and abundant taxa in the rumen and the human large intestine. Despite the naming, these clusters encompass many bacteria outside the genus Clostridium.

Overview

Clostridium contains around 250 species that include common free-living bacteria, as well as important pathogens. The main species responsible for disease in humans are:
Bacillus and Clostridium are often described as Gram-variable, because they show an increasing number of gram-negative cells as the culture ages.
Clostridium and Bacillus are both in the phylum Firmicutes, but they are in different classes, orders, and families. Microbiologists distinguish Clostridium from Bacillus by the following features:
Clostridium and Desulfotomaculum are both in the class Clostridia and order Clostridiales, and they both produce bottle-shaped endospores, but they are in different families. Clostridium can be distinguished from Desulfotomaculum on the basis of the nutrients each genus uses.
Glycolysis and fermentation of pyruvic acid by Clostridia yield the end products butyric acid, butanol, acetone, isopropanol, and carbon dioxide.
The Schaeffer-Fulton stain can be used to distinguish endospores of Bacillus and Clostridium from other microorganisms. There is a commercially available polymerase chain reaction test kit for the detection of C. perfringens and other pathogenic bacteria.

Treatment

In general, the treatment of clostridial infection is high-dose penicillin G, to which the organism has remained susceptible. Clostridium welchii and Clostridium tetani respond to sulfonamides. Clostridia are also susceptible to tetracyclines, carbapenems, metronidazole, vancomycin, and chloramphenicol.
The vegetative cells of clostridia are heat-labile and are killed by short heating at temperatures above 72–75 °C. The thermal destruction of Clostridium spores requires higher temperatures and longer cooking times. 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. The addition of lysozyme, nitrate, nitrite and propionic acid salts inhibits clostridia in various foods.
Fructooligosaccharides such as inulin, occurring in relatively large amounts in a number of foods such as chicory, garlic, onion, leek, artichoke, and asparagus, have a prebiotic or bifidogenic effect, selectively promoting the growth and metabolism of beneficial bacteria in the colon, such as bifidobacteria and lactobacilli, while inhibiting harmful ones, such as clostridia, fusobacteria, and bacteroides.

History

In the late 1700s, Germany experienced a number of outbreaks of an illness that seemed connected to eating certain 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.
Circa 1880, in the course of studying fermentation and butyric acid synthesis, a scientist surnamed Prazmowski first assigned a binomial name to Clostridium butyricum. The mechanisms of anaerobic respiration were still not yet well elucidated at that time, so taxonomy of anaerobes was still nascent.
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.

Use