Clostridium Study Guide PDF

VMMI216P Clostridium species Gram positive spore forming CLOSTRIDIUM SPECIES  Introduction The clostridia are large anaerobic, gram-positive, motile rods. Many decompose proteins or form toxins, and some do both. Their natural habitat is the soil or the intesti...

VMMI216P Clostridium species Gram positive spore forming CLOSTRIDIUM SPECIES  Introduction The clostridia are large anaerobic, gram-positive, motile rods. Many decompose proteins or form toxins, and some do both. Their natural habitat is the soil or the intestinal tract of animals and humans, where they live as saprophytes.  Introduction Among the pathogens are the organisms causing botulism, tetanus, gas gangrene, and pseudomembranous colitis.  Clostridia Clostridium tetani: tetanus; Clostridium botulinum: botulism; Clostridium perfringens: gas gangrene; and Clostridium difficile: pseudomembranous colitis. Other clostridia are also found in mixed anaerobic infections in humans  Morphology and Identification A. Typical Organisms Spores of clostridia are usually wider than the diameter of the rods in which they are formed. In the various species, the spore is placed centrally, subterminally, or terminally. Most species of clostridia are motile and possess peritrichous flagella.  B. Culture Clostridia are anaerobes and grow under anaerobic conditions; a few species are aerotolerant and also grow in ambient air. The clostridia grow well on the blood-enriched media or other media used to grow anaerobes  C. Colony Forms Some clostridia produce large raised colonies (eg, C perfringens); others produce smaller colonies (eg, C tetani). Atlas.sund.ku.dk  D. Growth Characteristics Clostridia can ferment a variety of sugars; many can digest proteins. These metabolic characteristics are used to divide the Clostridia into groups, saccharolytic or proteolytic.  D. Growth Characteristics Milk is turned acid by some and digested by others and undergoes “stormy fermentation” (i.e, clot torn by gas) with a third group (eg, C perfringens).  E. Antigenic Characteristics Clostridia share some antigens but also possess specific soluble antigens that permit grouping by precipitin tests or other assays.  CLOSTRIDIUM BOTULINUM C botulinum, which causes botulism, is worldwide in distribution; it is found in soil and occasionally in animal feces. Types of C botulinum are distinguished by the antigenic type of toxin they produce.  CLOSTRIDIUM BOTULINUM Spores of the organism are highly resistant to heat, withstanding 100°C for several hours. Heat resistance is diminished at acid pH or high salt concentration  Toxin During the growth of C botulinum and during autolysis of the bacteria, toxin is liberated into the environment. Seven antigenic varieties of toxin (A–G) are known. Types A, B, E, and F are the principal causes of human illness. Types A and B have been associated with a variety of foods and type E predominantly with fish products  Toxin Type C produces limberneck in birds; type D causes botulism in mammals. Clinical symptoms of limberneck (ruffled or quivering feathers, feathers that are easily pulled out, and labored breathing) Type G is not associated with the disease.  Pathogenesis The most common offenders of C botulinum are spiced, smoked, vacuum packed, or canned alkaline foods that are eaten without cooking. In such foods, spores of C botulinum germinate; that is, under anaerobic conditions, vegetative forms grow and produce toxin.  In infant botulism, honey is the most frequent vehicle of infection. The pathogenesis differs from the way that adults acquire infection. The infant ingests the spores of C botulinum (or C butyricum or C baratii), and the spores germinate within the intestinal tract.  The vegetative cells produce toxin as they multiply; the neurotoxin then gets absorbed into the bloodstream. The toxin acts by blocking release of acetylcholine at synapses and neuromuscular junctions  Clinical Findings Symptoms begin 18–24 hours after ingestion of the toxic food, with visual disturbances (incoordination of eye muscles, double vision), inability to swallow, and speech difficulty; Signs of bulbar paralysis are progressive, and death occurs from respiratory paralysis or cardiac arrest.  Gastrointestinal symptoms are not regularly prominent. There is no fever. The patient remains fully conscious until shortly before death. The mortality rate is high. Patients who recover do not develop antitoxin in the blood.  In the United States, infant botulism is as common as or more common than the classic form of paralytic botulism associated with the ingestion of toxin-contaminated food. The infants in the first months of life develop poor feeding, weakness, and signs of paralysis (floppy baby).  Infant botulism may be one of the causes of sudden infant death syndrome. C botulinum and botulinum toxin are found in feces but not in serum  Diagnostic Laboratory Tests Toxin can often be demonstrated in serum, gastric secretions, or stool from the patient, and toxin may be found in leftover food. Mice injected intraperitoneally with such specimens from these patients die rapidly. The antigenic type of toxin is identified by neutralization with specific antitoxin in mice.  Diagnostic Laboratory Tests In infant botulism, C botulinum and toxin can be demonstrated in bowel contents but not in serum. Other methods used to detect toxin include ELISAs and PCR, but the latter may detect organisms that carry the gene but do not express toxin.  Treatment Potent antitoxins to three types of botulinum toxins have been prepared in horses. Because the type responsible for an individual case is usually not known, trivalent (A, B, E) antitoxin must be promptly administered intravenously with customary precautions.  Treatment Adequate respiration must be maintained by mechanical ventilation if necessary. These measures have reduced the mortality rate from 65% to below 25%. Although most infants with botulism recover with supportive care alone, antitoxin therapy is recommended.  Epidemiology, Prevention, and Control Because spores of C botulinum are widely distributed in soil, they often contaminate vegetables, fruits, and other materials. A large restaurant-based outbreak was associated with sautéed onions. When such foods are canned or otherwise preserved, they either must be sufficiently heated to ensure destruction of spores or must be boiled for 20 minutes before consumption.  Epidemiology, Prevention, and Control Strict regulation of commercial canning has largely overcome the danger of widespread outbreaks, but commercially prepared foods have caused deaths. A chief risk factor for botulism lies in home-canned foods, particularly string beans, corn, peppers, olives, peas, and smoked fish or vacuum-packed fresh fish in plastic bags  Epidemiology, Prevention, and Control Toxic foods may be spoiled and rancid, and cans may “swell,” or the appearance may be innocuous. The risk from home-canned foods can be reduced if the food is boiled for more than 20 minutes before consumption. Toxoids are used for active immunization of cattle in South Africa.  Epidemiology, Prevention, and Control Botulinum toxin is considered to be a major agent for bioterrorism and biologic warfare. CLOSTRIDIUM TETANI CLOSTRIDIUM TETANI  Background C tetani, which causes tetanus, is worldwide distributed in the soil and in the feces of horses and other animals. Several types of C tetani can be distinguished by specific flagellar antigens. All share a common O (somatic) antigen, which may be masked, and all produce the same antigenic type of neurotoxin, tetanospasmin.  Toxin The vegetative cells of C tetani produce the toxin tetanospasmin. The toxin initially binds to receptors on the presynaptic membranes of motor neurons. It then migrates by the retrograde axonal transport system to the cell bodies of these neurons to the spinal cord and brainstem.  Extremely small amounts of toxin can be lethal for humans.  Pathogenesis C tetani is not an invasive organism. The infection remains strictly localized in the area of devitalized tissue (wound, burn, injury, umbilical stump, surgical suture) into which the spores have been introduced.  Pathogenesis The volume of infected tissue is small, and the disease is almost entirely a toxemia. Germination of the spore and development of vegetative organisms that produce toxin are aided by (1) necrotic tissue, (2) calcium salts, and (3) associated pyogenic infections, all of which aid establishment of low oxidation-reduction potential.  Pathogenesis The toxin released from vegetative cells reaches the central nervous system and rapidly becomes fixed to receptors in the spinal cord and brainstem and exerts the actions described.  Clinical Findings The incubation period may range from 4 to 5 days to as many weeks. The disease is characterized by tonic contraction of voluntary muscles. Muscular spasms often involve first the area of injury and infection and then the muscles of the jaw (trismus, lockjaw), which contract so that the mouth cannot be opened.  Clinical Findings Gradually, other voluntary muscles become involved, resulting in tonic spasms. Any external stimulus may precipitate a tetanic generalized muscle spasm. The patient is fully conscious, and pain may be intense.  Clinical Findings Death usually results from interference with the mechanics of respiration. The mortality rate in generalized tetanus is very high.  Diagnosis The diagnosis rests on the clinical picture and a history of injury, although only 50% of patients with tetanus have an injury for which they seek medical attention. The primary differential diagnosis of tetanus is strychnine poisoning.  Diagnosis Anaerobic culture of tissues from contaminated wounds may yield C tetani, but neither preventive nor therapeutic use of antitoxin should ever be withheld pending such demonstration. Proof of isolation of C tetani must rest on production of toxin and its neutralization by specific antitoxin  Culture Robison cooked meat broth: growth in cooked meat broth is subcultured in blood agar after 24 to 48 hours. Blood agar- Aerobic and anaerobic cultures are made on fresh and heated blood agar Blood agar is incubated anaerobically for 48hrs to 72 hours. Most strains produce B haemolysis on BAP  Prevention and Treatment Prevention of tetanus depends on: (1) active immunization with toxoids, (2) proper care of wounds contaminated with soil (3) prophylactic use of antitoxin, and (4) administration of penicillin  Prevention and Treatment The intramuscular administration of 250–500 units of human antitoxin (tetanus immune globulin) gives adequate systemic protection (0.01 unit or more per milliliter of serum) for 2–4 weeks. It neutralizes the toxin that has not been fixed to nervous tissue. Active immunization with tetanus toxoid should accompany antitoxin prophylaxis  Prevention and Treatment Patients who develop symptoms of tetanus should receive muscle relaxants, sedation, and assisted ventilation. Sometimes they are given very large doses of antitoxin (3000– 10,000 units of tetanus immune globulin) intravenously in an effort to neutralize toxin that has not yet been bound to nervous tissue  Prevention and Treatment Penicillin strongly inhibits the growth of C tetani and stops further toxin production. Antibiotics may also control associated pyogenic infection.  Prevention and Treatment Associated pyogenic infection. When a previously immunized individual sustains a potentially dangerous wound, an additional dose of toxoid should be injected to restimulate antitoxin production. This “recall” injection of toxoid may be accompanied by a dose of antitoxin if the patient has not had current immunization or boosters or if the history of immunization is unknown.  Control Tetanus is a totally preventable disease. Universal active immunization with tetanus toxoid should be mandatory. Tetanus toxoid is produced by detoxifying the toxin with formalin and then concentrating it.  Control Aluminum salt–adsorbed toxoids are used. Three injections comprise the initial course of immunization followed by another dose about 1 year later. Initial immunization should be carried out in all children during the first year of life.  Control A “booster” injection of toxoid is given upon entry into school. Thereafter, “boosters” can be spaced 10 years apart to maintain serum levels of more than 0.01 unit antitoxin per milliliter.  Control In young children, tetanus toxoid is often combined with diphtheria toxoid and acellular pertussis vaccine. Control measures are not possible because of the wide dissemination of the organism in the soil and the long survival of its spores.  Home work Self study on the following types of clostridia CLOSTRIDIA THAT PRODUCE INVASIVE INFECTIONS CLOSTRIDIUM DIFFICILE AND DIARRHEAL DISEASE A quiz will be conducted on the above mentioned microorganism.