The Gram positive spore-forming anaerobic bacilli:

Clostridium speciesMicroscopic characteristics:Gram-positive spore-forming, anaerobic large bacilli, 5 µm x 1 µm.

Some members are saprophytic in soil and sewage; others are commensals in the intestine of man and animals.

All organism can grow on blood agar under anaerobic conditions.

The most important pathogens are: Clostridium tetani, Clostridium perfringens, Clostridium botulinum and Clostridium difficili.

Large terminal spores of Clostridium tetani giving drum-stick appearance, appear in smears of wound discharge.

a

Oval central or subterminal spores of Clostridium botulinum:

a

Cultural characteristics:

All species are obligatory anaerobic.The optimum growth occurs at 7.3 PH and 37C temperature. On blood agar, C. perfringes produce smooth, large, regular, convex, and slightly opaque colonies, and zone of complete hemolysis surrounded by wider zone of incomplete hemolysis.

C.tetani can also be cultivated on blood and nutrient agar, colonies show fine branching projections with raised central part and filamentous edge.

Beta hemolytic colonies of C. perfringes surrounded by alpha hemolysis.

a

Beta hemolytic colonies of Clostridium tetani.

a

Biochemical identification: All species are Catalase and oxidase negative.

All species neither produce lipases nor proteases.

C.perfringens ferments lactose and produce Lecithinase. Other species can not ferment lactose and Lecithinase negative.

Lecithinase production and lactose fermentation of Clostridium perfringens.

A

Pathogenesis:

Clostridium includes common free-living bacteria as well as important pathogens. There are four main species responsible for disease in humans:

C. perfringens, causes a wide range of symptoms, from food poisoning to gas gangrene.

a

Gangrene is necrosis and subsequent decay of body tissues caused by infection or thrombosis or lack of blood flow. It is usually the result of critically insufficient blood supply sometimes caused by injury and subsequent contamination with bacteria. This condition is most common in the extremities. The best of all possible treatments is revascularization (restoration of blood flow) of the affected organ, which can reverse some of the effects of necrosis and allow healing.

Diabetic ulceration with central 'dry' gangrene and toward the edges wet gangrene with some ascending cellulitis:

A

Tetanus (lockjaw disease):

Etiology: Clostridium tetani.Tetanus affects skeletal muscle.The other type of striated muscle, cardiac or heart muscle cannot be tetanized due to intrinsic electrical properties. In recent years, approximately 11% of reported tetanus cases have been fatal. The highest mortality rates are in unvaccinated persons and persons over 60 years of age. C. tetani, the bacteria that causes tetanus, is recovered from the initial wound in only about 30% of cases.

A-Muscle spasms in a patient suffering from tetanus.B-An infant suffering from neonatal tetanus

A B

Botulism:

C. botulinum, an organism producing a toxin in food that causes botulism. Botulism (from the Latin word botulus, "sausage") is a rare, but serious paralytic illness caused by a nerve toxin, botulin, that is produced by the bacterium Clostridium botulinum. Botulinic toxin is one of the most powerful known, with a lethal dose of a microgram. It acts by blocking nerve function and leads to respiratory and musculoskeletal paralysis.

There are three main kinds of Botulism:

Food borne botulism is a form of food borne illness and is caused by eating foods that contain the botulinum toxin.

Infant botulism is caused by consuming the spores of the botulinum bacteria, which then grow in the intestines and release toxin. Wound botulism is caused by toxin produced from a wound infected with Clostridium botulinum.

C. difficile , which can overgrow other bacteria in the gut during antibiotic therapy, can cause pseudomembranous colitis.

A