Medical Microbiology: Clostridium PDF

**Clostridium** **[Occurrence:-]** - Clostridia are spor forming bacteria - naturally inhabit the soil and the intestinal tracts of humans and animals. - Many species are saprophytes. - Under certain conditions, several species cause 1. **Gas gangrene** 2. **Tetanus** 3. **Bot...

**Clostridium** **[Occurrence:-]** - Clostridia are spor forming bacteria - naturally inhabit the soil and the intestinal tracts of humans and animals. - Many species are saprophytes. - Under certain conditions, several species cause 1. **Gas gangrene** 2. **Tetanus** 3. **Botulism** 4. **Pseudomembranous** **colitis**. **[Morphology and culturing:-]** - All are large, Gram-positive rod bacteria about 1 µm thick and 3--8 µm in length - Many cells in older cultures show a Gram-negative reaction. - With the exception of *C. perfringens*, clostridia are flagellated. **The Pathogens That Cause Gas Gangrene** **(Clostridial Myonecrosis) and Anaerobic Cellulitis** **[Pathogen spectrum]** :- The pathogens that cause these clinical pictures include *Clostridium perfringens* which is The most frequent causative pathogen in gas gangrene **[Toxins and Enzymes :-]** The toxins produced by invasive clostridia show : - Necrotizing - hemolytic - lethal activity. They also produce following enzymes all of which destroy tissue structures, resulting in accumulations of toxic metabolites. - Collagenases - Proteinases - Dnases - Lecithinases - hyaluronidas **[Pathogenesis and clinical picture:- ]** Two such infections of differing severity are described below: 1. **[Anaerobic cellulitis]**. - Infection restricted to the fascial spaces that does not affect muscular. - Gas formation in tissues causes a cracking under the skin known as crepitus. - There is no toxemia. 2. **Gas gangrene (clostridial myonecrosis).** - An aggressive infection of the musculature with myonecrosis and toxemia. - The incubation period varies from hours to a few days. **[Therapy]**. - Primary treatment is surgical, with Penicillins and Cephalosporins). - Treatment with hyperbaric chamber O~2~ in special centers has prove effective patients breathe pure O2 through a tube or mask in a pressure chamber **Clostridium tetani (Tetanus)** - Tetanus (lockjaw) is an acute clostridial disease - its clinical manifestations do not result directly from the invasive infection - It is caused by a strong neurotoxin. **[Toxin]** :- - Tetanospasmin consists of two polypeptide chains linked by a disulfide bridge. - The heavy chain binds specifically to neuron receptors. - The light chain is a zinc-metalloprotease that is responsible for proteolysis of components of the neuroexocytosis apparatus in the synapses of spinal cord. This stops transmission of inhibitory efferent impulses from the cerebellum to the motor end plates. **[Pathogenesis and clinical picture. ]** - These pathogens invade tissues following injuries - Given anaerobic conditions, they proliferate and produce the toxin - This toxin reaches to spinal cord or brain. - The clinical picture resulting from the effects of the toxin - It is characterized by increased muscle tone and spasms induced by visual or acoustic stimuli. - The cramps often begin in the facial musculature then spread to neck and back muscles **[Therapy. :-]** - Antitoxic therapy with immune sera is applied following a wound cleaning. **Clostridium botulinum (Botulism)** - **Foodborne botulism** is not an infection, but rather an intoxication, that is, the toxin is ingested with food. - **Infant botulism** involves ingestion of spores - **Wound botulism** results from infection of a wound. **[Toxin]**. :- - The very strong botulinum neurotoxin is a heat-labile protein. - Seven toxigenic types are differentiated, each of which produces an immunologically distinct form of botulinum toxin. - Types A, B, and E cause poisoning in humans. **[Pathogenesis and clinical picture. ]** - Classic botulism results from eating spoiled foods in which the toxin has been produced under anaerobic conditions by *C. botulinum*. - The toxin is absorbed in the gastrointestinal tract, and then transported to the peripheral nervous system in the bloodstream. - Within a hours or days paralysis symptoms occur, especially in the nerves of the head. - Frequent symptoms include seeing double, difficulty swallowing and speaking, constipation, and dry mucosa. - Lethality rates range from 25--70%, depending on the amount of toxin ingested. - Death usually results fro respiratory paralysis. ***Clostridium* *difficile* (Pseudomembranous Colitis)** - *C. difficile* occurs in the fecal flora of 1--4% of healthy adults and in 30--50% of children during the first year of life. - The pathological mechanism is based on formation of two toxins. 1. Toxin A is an enterotoxin that causes a dysfunction characterized by increased secretion of electrolytes and fluids. 2. Toxin B is a cytotoxin that damages the mucosa of the colon. - The clinical course includes 1. Fever 2. Diarrhea 3. spasmodic abdominal pains. - Toxins A and B can also be detected with immunological test kits - specific therapy is not required in many cases. Antibiotic treatment is indicated in severe cases. - The agent of choice is currently metronidazole.