CLOSTRIDIUM ANAEROBIC, G+VE, SPORE FORMING BACILLI By Radwan A. Baabbad

Some members of the genus Clostridium are saprophytes in soil, sewage and water. Others are commensals in the intestine of man & animals. The important members that cause disease in man are: Cl. tetani causing tetanus. Cl. botulinum botulism. Cl. Perfringens causing gas gangrene & food poisoning Cl. Difficile causing pseudomembranous colitis & antibiotic associated diarrhoea.

Clostridium tetani It is found as parasite in the gastrointestinal tract of animals & as parasite in manured soil. It causes tetanus in man & animals. Morphology: G+ve motile bacilli swollen at one end due to terminal spherical projecting spores; “ drum-stick appearance”. Cultural characters: Strict anaerobes, grow on nutrient agar & blood agar causing haemolysis due to tetanolysin toxin. The organism grows readily on Robertson cooked meat medium.

Toxin production: Cl.Tetani has a neurotoxin “tetanospasmin” that gives it the pathogenicity, which is a polypeptide that exists as one antigenic type. The toxin is released from the site of the wound & diffuses via the blood stream to the peripheral nervous system and reaches the CNS by retrograde axonal transport. The toxin binds to gangliosides receptors and blocks the release of inhibitory mediators ( glycine & gama-aminobutyric acid GABA ). Motor neurons are left under no inhibitory control & undergo sustained excitatory discharge, causing the characteristic motor spasms of tetanus.

The toxin exerts its effect on the spinal cord, brain stem, peripheral nerves & on muscles. Thus leading to generalized muscular spasm, hyper-reflexia, seizures and spastic paralysis.

TETANUS Infection occurs by contamination of wounds with street dust containing the spores, contaminated surgical wound, gun shot, or an infected umbilical stump or circumcision leading to ”tetanus neonatorum” The spores germinate in the wound releasing the toxin “tetanospasmin” which starts its action. Germination is enhanced by the presence of necrotic tissue or associated pyogenic infection.

The disease is characterized by convulsive tonic contractions of voluntary muscles including; spasm in jaw muscles leading to trismus (lock jaw), facial spasm (sardonic grin), arching of the back. Death rate is high & occurs due to respiratory or cardiac failure. An attack of tetanus dose not provide immunity to future attacks ?

Diagnosis On clinical suspicion treatment with anti toxin should be started without waiting for lab diagnosis which is done for confirmation. Wound exudate aspirated from deep site of the wound is examined microscopically for the presence of gram + bacilli with drum-stick appearance. The exudate is cultured on BA incubated anaerobically & on Robertson cooked meat medium. The organism is identified on lab animals, which is neutralized by specific antitoxin.

Prevention & control Tetanus is totally preventable disease. Prophylactic immunization is the only way for control Active immunization: Alum precipitated tetanus toxoid is given in combination with diphtheria toxoid and pertussis vaccine “DTP” in 3 intramuscular injection at the age of 2,4 & 6 monthes.

A booster dose is given a year later & another upon school entry. A booster dose of tetanus & diphtheria (DT) is recommended every 10 years. Individuals wounded with a previous vaccination 5 years or more should receive a booster dose. Boosters are recommended for pregnant women to prevent labour infection & provide immunity for newborn.

Passive immunization: Antitoxin is given to wounded persons without previous history of vaccination or those immunized more than 10 years ago. Human tetanus immune globulin ( HTIG) is the antitoxin made in humans to avoid hypersensitivity reaction that occur when antitoxin made in horses is used. Intramuscular injection of 250-500 IU from HTIG will give protection for 2- 4 weeks.

Treatment Antitoxin should be given at once to suspect cases to neutralize any toxin that did not fix to the CNS. HTIG is given in a dose of 3000-10,000 IU divided into 3 equal portions, given intramuscularly in three different sites at the same time. Proper care of the wound is very important. Penicillin or metronidazole are given in big doses to eliminate the organism from tissues & to treat pyogenic infections. An adequate airway must be maintained and respiratory support given. Benzodiazepines e.g. valium, should be given to prevent spasm.

Clostridium botulinum G+ve large straight rods, motile, non-capsulated, spore-forming, anaerobic bacteria which grow on simple media. Found in soil, intestinal tract of domestic animals & inadequately sterilized canned food. Canning provides proper anaerobic conditions for growth & production of exotoxin. The organism causes botulism which is a type of food poisoning.

Botulinum toxin: Cl. Botulinum produces a polypeptide neurotoxin . The toxin is absorbed from the gut & is carried via the blood then binds to the presynaptic nerve endings of the peripheral nervous system & cranial nerves, where it blocks the release of acetylcholine at the neuromuscular junction leading to flaccid paralysis. There are 7 antigenic types (A-G), A, B, E & F causes botulism in man. The toxin is heat labile ( can be destroyed by 20 min. boiling)

Botulism There are three clinical forms of botulism: Foodborne botulism: 1-2 days after ingestion of ready-made toxin in food (canned). Initially, bulbar paralysis manifesting as diplopia, dysphagia & respiratory muscle failure. There is no diarrhoea, vomiting or fever.

Wound botulism: spores contaminate a wound, germinate & produce toxin at the site. Infant botulism: “floppy baby” occurs due to ingestion of spores in baby food, where they germinate in gut & produce toxin. Some cases have been attributed to the presence of the spores in honey. It affects infants below 6 months when the colonization resistance of the gut is poor. They develop poor feeding, weakness or paralysis & may need respiratory support but usually recover spontaneously. However, it may cause sudden infant death syndrome.

Diagnosis: The toxin can be directly detected by passive haemagglutination or PCR in patient serum or food remnants. In infant botulism, it can be detected in bowel contents. 2. The toxin in patient’s serum or food remnants can be injected into mice, which will die with generalized flaccid paralysis. Typing of the toxin can be done by nutralization with specific antitoxin in mice “mouce protection test”.

Treatment & prevention Trivalent antitoxin ( types A,B & E) is administered I.V. within 12 h after ingestion before the toxin binds to the tissues. An adequate airway must be maintained and respiratory support given. Prevention is by careful sterilization of food before canning. Swollen cans should be discarded. Honey should not be given to infants.