GENUS CLOSTRIDIUM
Classification
Domain: Bacteria
Phylum: Firmicutes
Class: Clostridia
Order: Clostridiales
Family: Clostridiaceae
Genus: Clostridium
Introduction
In this genus spore forming anaerobic rods are placed. The spores are wider than the bacillary bodies, giving the bacillus a swollen appearance, resembling a spindle-hence the name Clostridium (from kloster, meaning spindle). By virtue of the resistant spore which they produce, the natural habitat of the majority of the species is soil and intestinal tracts of animals. Species are pathogenic to human and animals in which they produce distinct types of disease by the action of potent exotoxins produced either within or outside the animal body.
The spores of all anaerobic bacilli are prevalent in soil; consequently, the diseases which are caused by this group of bacteria are often called as ‘soil-borne infections’.
Clostridia can produce disease only when the conditions are appropriate. Their invasive powers are limited. Pathogenic clostridia form powerful exotoxins. Clostridium botulinum is virtually non-invasive and non-infectious. Botulism is due to the ingestion of preformed toxin in food. Clostridium tetani has poor invasive property and multiplication of bacteria is confined to primary site of lodgement.
History
Tetanus has been known from very early times, been described by Hippocrates.
Rosenbach in 1886, demonstrated a slender bacillus with round terminal spores in a case of tetanus.
Kitasato in 1889 isolated Clostridium tetani in pure culture and reproduced the disease in animals by inoculation of pure culture.
Clostridium botulinum was first isolated by Van Ermengam in 1896 from a piece of ham, was the cause of an outbreak of botulism. Clostridium botulinum denotes a group of bacteria that produce extremely potent neurotoxins.
Important species and diseases caused by Genus Clostridium
| Species | Disease | Host |
| Clostridium chauvoei | Black quarter (black leg) | Cattle & sheep |
| Wound infections (gas gangrene) | Many species | |
| Clostridium septicum | Maligant edema | Many species |
| Braxy | Sheep | |
| Clostridium haemolyticum | Bovine bacillary haemoglobinuria | Cattle |
| Clostridium novyi (type A) | Wound infection (gas gangrene) | Sheep & cattle |
| (Type B) | Black disease(necrotic hepatits) | Sheep & cattle |
| (Type C) | Osteomyelitis | Water buffalo |
| Clostridium botulinum | Botulism | Many species |
| Clostridium tetani | Tetanus | Many species |
| Clostridium perfringens /Clostridium Welchii (Type A) |
Food poisoning, gas gangrene, enterotoxaemia jaundice(Yellow lamb disease)and necrotic enteritis. | Human, lambs & chicken |
| (Type B) | Lamb dysentery | Lamb (Under 3 weels old) |
| (Type C) | Haemorrhagic enterotoxaemia (Clostridial enteritis), Necrotic enteritis, Struck. | Piglets, lambs, calves,sheep, foals, chicken & goat |
| (Type D) | Pulpy kidney disease | Sheep |
| (Type E) | Enterotoxaemia | Calves and lambs |
| Clostridium difficile | Pseudomembranous colitis | Human, monkeys and pigs |
| Avian Diseases | ||
| Clostridium botulinum | Botulism(limberneck) | Chickens |
| Clostridium colinum | Ulcerative enteritis (quail disease) | Chicken, quail, pigeons & other birds |
| Clostridium perfringens | Necrotic enteritis, gangrenous dermatitis(Malignat edema) | Chickens & turkeys |
| Clostridium septicum | Gangrenous dermatitis | Chickens |
Classification of Clostridia
A. Classification of Clostridia based on spore formation
1.Central or equatorial :- giving the bacillus a spindle shape.
eg. Clostridium bifermentans
2. Subterminal:- bacillus appering club shaped.
eg. Clostridium perfringens
3.Oval and terminal:- resembling a tennis racket
eg. Clostridium tertium
4. Spherical and terminal:-giving a drumstick appearance.
eg. Clostridium tetani
B. Classification of clostridia by kind of disease produced
1. Histotoxic clostridia: causes a variety of tissue (often muscle) infections frequently following wounds or other trauma.
e.g.,Clostridium chauvoei, Clostridium septicum, Clostridium novyi
2. Hepatotoxic clostridia: produces their toxins in the liver, thus resulting in disease Bacillary haemoglobinuria and Black disease.
e.g.,Clostridium haemolyticum, Clostridium sordellii, Clostridium colinum, Clostridium piliforme
3. Enterotoxigenic clostridium: produces mainly enterotoxaemia and food poisoning although they are occasionally histotoxic.
e.g.,Clostridium perfringens (type A to type E).
4. Neurotoxic clostridia: cause the disease by the production of the potent exotoxins (Neurotoxins).
e.g.,Clostridium tetani, Clostridium botulinum
C. Morphological and biochemical classification of Clostridia
| Proteolytic predominating | Saccharolytic predominating | Slightly proteolyticbut not saccharolytic | Saccharolytic but not proteolytic | Neither proteolytic nor saccharolytic |
| Clostridium bifermentans | Clostridium perfringens |
Clostridium tetani |
Clostridium fallax |
Clostridium cochlearum |
| Clostridium botulinum | Clostridium septicum |
Clostridium botulinum |
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| Clostridium histolyticum | Clostridium chauvoei |
Clostridium tertium |
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| Clostridium sordelli |
Clostridium novyi |
Clostridium tetanomorphum |
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| Clostridium sporogenes | Clostridium difficile |
Clostridium sphenoides |
Morphology
Clostridia are highly pleomorphic, rod shaped; long filaments and forms are common.
The clostridia are motile with peritrichous flagella except Clostridium welchii & Clostridium tetani type VI are non motile.
Measures 0.4 to 1.2 u by 3u to 8 u in length.
Gram positive rods. Clostridia are easily stained. They are Gram positive but in older cultures.
Spore forming (Central, terminal & subterminal)
Non-capsulated (except Clostridium welchii, Clostridium perfringens and Clostridium butyricum)
Clostridia are anaerobic , get off when exposed to oxygen, because anerobic bacteria lack catalase, super oxide dismutase(SOD) and nonspecific peroxidase enzymes, do not have ability to degrade oxygen radicals i.e. H2O2. The sensitivity to oxygen varies in different species. Some (for example , Clostridium novyi )are exacting anaerobes and get off on exposure to oxygen, while some others (for example, Clostridium histolyticum) are aerotolerant and may even grow aerobically. More important than the absence of oxygen is the provision of a sufficiently low redox potential (Eh) in the medium. This can be achieved by adding reducing substances such as unsaturated fatty acids, ascorbic acids, glutathione , cysteine, thioglycollic acids, alkaline glucose, sulphites or metallic iron. A small concentrations of CO2 appears to enhance growth.
G+C content of DNA is 22 – 32 mol%.
The optimum temperature for pathogenic Clostridia is 370C. Some saprophytic Clostridia are thermophilic and others psychrophylic. The optimum pH is 7-7.4.
Resistance
The endospores of clostridia are highly resistant to various physical and chemical agents, including disinfectant. In this respect, they are similar to the spores produced by Bacillus anthracis, in that 30 min. of boiling may be required to kill the spores of Clostridium botulinum; autoclaving at 121oC for 20 min. is lethal. The vegetative forms of the clostridia are susceptible to common is disinfectant.