There are four cultural groups of Cl. botulinum. (see classification section)

Strains are generally considered as members of this species on the basis of their production of one of the serological types of botulinum toxins. Taxonomically the organisms fall into four distinct groups.

CLASSIFICATION

Group I: The slightly curved rods have peritrichous flagellae, and form subterminal ellipsoidal spores, which distend the rods slightly. The GC content of the DNA is 26-28 mol%.

Group II: The straight rods have peritrichous flagellae, and form subterminal ellipsoidal spores. The spores of Cl. botulinum type E have characteristic appendages. The GC content of the DNA is 26-28 mol%.

Group III: The straight rods have peritrichous flagellae, and form subterminal ellipsoidal spores. The GC content of the DNA is 26-28 mol%.

Group IV (Cl. argentinense): The straight rods have peritrichous flagellae, and form subterminal ellipsoidal spores. The GC content of the DNA is 26-28 mol%.

BIOCHEMISTRY

Group I: They grow optimally at 37°C, are proteolytic and produce A, B or F toxins. They can ferment glucose and fructose. Products include acetic and butyric acids and alcohols. They liquify gelatin, digest casein and cooked meat, produce H2S and lipase but not indole or urease.

Group II: They grow optimally at 30°C, are not proteolytic and produce B, E or F toxins. They can ferment many carbohydrates but not lactose, mannitol, melibiose and salicin. Products are mainly acetic and butyric acids. They liquify gelatin, but do not digest casein and cooked meat, produce H2S, lipase, indole or urease.

Group III: They grow optimally at 37-40°C; they vary from being slightly to non-proteolytic and produce C1, C2 or D toxins. They ferment glucose, glycerol, inositol, ribose and xylose and are variable on fructose, galactose, maltose and melibiose. Products are mainly propionic and butyric acids. They liquify gelatin, but may only barely digest casein and cooked meat, they do not produce H2S, indole or urease, but produce lipase.

Group IV (Cl. argentinense): Their growth range is 25-45°C; they are proteolytic and produce G toxin. They do not ferment any carbohydrates, but can use citrate and some amino acids as energy source. They liquify gelatin, and digest casein and cooked meat, they produce H2S, but not indole, lipase or urease.

Some of the toxins such as C1 and D are bacteriophage induced, while C2 is not.

Species within Groups I and II share antigens.

VIRULENCE FACTORS

Neurotoxins:

These are the main toxins of these organisms. They prevent the release of acetyl choline at the neuromuscular junction.

NORMAL FLORA

Cl. botulinum can form part of normal flora of the large intestine of humans and animals.

PATHOGENS

Intestinal Infections:

Botulism is generally caused by ingestion of food containing preformed toxins, generally due to inadequate preparation.

Infant botulism is caused generally by infants under 9 months ingesting organisms, which produce the toxins in the large intestine.

Extraintestinal Infections:

Wound botulism is due to the organisms getting into wounds.

Animal Infections:

Group II strains cause outbreaks of botulism in ducks throughout the world. They also affect other avian species including pheasants and chickens.

LABORATORY ID

The most important means of detecting botulism is by detecting the toxin(s). This usually involves an animal test including neutralisation to test which antitoxin protects the animal.

The organisms can be easily recovered using cooked meat and growth in anaerobic conditions, but are generally only present in small numbers or not at all. Alcohol or heat shock may be used to kill vegetative (not spores) contaminating bacteria and cause the spores to germinate.

ENVIROMENTAL

Cl. botulinum spores can survive for long periods in soils and water and have been recovered from these environments.

INDUSTRIAL USES

Apart from the production of toxins for antitoxin development there are no industrial uses. They have been suggested as potential germ-warfare agents.

Botulinum toxin has also been suggested as a means of topically treating some nervous conditions, such as uncontrolled blinking of the eyelids.

COSMETIC USES

Botulinum toxin (Botox) is used for cosmetic purposes.

VACCINES

Vaccination will not protect hosts from botulism, however passive immunisation with antibody is the treatment of choice for cases of botulism.

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