SPORE- FORMING BACILLI ANAEROBIC, GRAM-POSITIVE, SPORE-FORMING RACILLI ‘CLOSTRIDIUM’

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The important members that cause disease in man are:

1. CI. tetani causing tetanus.

2. CI. perfringens causing gas gangrene and food poisoning.

3. Cl. botulinum causing botulism, which is a type of food poisoning.

4. Cl. difficile causing pseudomembranous colitis & antibiotic associated diarrhea.

Clostridium tetani

· It causes tetanus in man and animals.

Morphology:

· Gram-positive motile bacilli

· Drum-stick appearance".

Cultural characters: Strict anaerobes. They grow on:

Blood agar producing ß-haemolysis

Robertson cooked meat medium.

Animal pathogenicity: When mice are injected shows spastic paralysis

TETANUS

Pathogenesis:

· Infection occurs by:

1. Contamination of wounds with street-dust.

2. Contaminated surgical wound

3. Gun shot wound

4. Infected umbilical stump leading to "tetanus neonatorum".

· Cl. tetani is not invasive organism. The infection remains localized in tissues. At the site of infection the spores germinate releasing the toxin that reaches the CNS causing spastic paralysis.

Generalized tetanus:

· The disease is characterized by convulsive tonic contractions of voluntary muscles including; spasm in jaw muscles leads to trismus (lock jaw), facial spasm (sardonic grin), pronounced arching of the back due to spasm of the muscles of the back

· Death occurs due to respiratory or cardiac failure.

Neonatal tetanus "tetanus neonatorum". The infection follows contamination, of the umbilical stump or circumcision wound of the newborn infants, by tetanus spores. It occurs if the mother is not immune.

Diagnosis:

· Specimens: Wound exudates

· Smear: are stained with Gram stain and examined microscopically for the presence of Gram-positive bacilli with drum-stick appearance.

· Culture: The exudate is cultured on blood agar incubated anaerobically, and on Robertson cooked meat medium.

· The organism is identified by its pathogenicity to laboratory animals (spastic paralysis).

Prevention and control: Tetanus is a totally preventable disease.

Active immunization: Tetanus toxoid "DPT" in three intramuscular injections at the age of 2, 4 and 6 months.

· A booster dose is given a year later and another upon school entry.

· A booster dose of tetanus and diphtheria (DT) is recommended every 10 years to maintain a good serum antitoxin level.

Passive immunization: Antitoxin is given to:

1. Wounded persons without previous history of vaccination.

2. Those immunized more than 10 years ago.

Treatment:

1. Antitoxin should be given at once to suspected cases

2. Proper care of the wound and surgical debridement.

3. Penicillin or metronidazole is given in big doses

4. An adequate airway and respiratory support given.

Clostridiurn perfringens

· It is associated with gas gangrene.

Morphology:

· Gram-positive large bacilli arranged singly or in pairs. .

· Spores are oval, subterminal and non-projecting.

· It is capsulated.

· It is non-motile.

Cultural characters:

· Obligate anaerobes.

· Colonies on blood agar show double zones of haemolysis

· They can be grown on cooked meat.

Biochemical activities

· They ferment glucose, lactose, maltose and sucrose producing acid and large amounts of gas.

· The organism causes rapid fermentation of lactose in litmus milk and the produced gas splits the clot “stormy clot reaction".

· Nagler’s reaction: All types of Cl. perfringens produce opalescence in egg yolk media due to production of lecithinase which causes a visible precipitate around the colonies.

Diseases caused by Cl. Perfringens:

1. Soft tissue infections which are subdivided into: Cellulites, Fasciitis or suppurative myositis, Myonecrosis or gas gangrene

2. Food poisoning.

GAS GANGRENE

Pathogenesis and clinical findings:

· The infection occurs when wounds are contaminated with soil containing the organism.

· The condition occurs in deep lacerated, devitalized wounds as in car accidents or war wounds.

· The presence of foreign bodies, aerobic pyogenic bacteria and decreased blood supply favour germination of spores.

· Vegetative cells multiply and ferment sugars producing large amounts of gas which distends the tissues and interferes with their blood supply leading to their death (necrosis and gangrene).

· Proteolytic clostridia digest dead tissues leading to change in colour and foul odour of the wound.

· The wound is oedematous, foul smelling, dark in colour with crepitations in the adjacent tissues.

Diagnosis:

· Specimens: Exudates, pus or tissues from deep sites of the wound.

· Smears: are stained by Gram’s; the presence of large Gram-positive rods is suggestive. Spores are rarely found.

· Cultures are made on cooked meat and on blood agar plates incubated anaerobically.

· Colonies that grow are further identified by:

¨ Morphology, Sugar fermentation, Stormy clot formation in litmus milk, Nagler’s reaction

· Animal inoculation: The injected limb shows oedema and crepitation.

Treatment and prevenyion:

1- Surgical debridement of devitalized tissues.

2– Penicillin in big doses in combination with metronidazole is used.

3- Hyperbaric oxygen therapy may be of value.

Clostridium botulinum

· It causes botulism, which is a type of food poisoning.

Morphology:

· Gram-positive large straight rods, motile, non-capsulated.

· Spores are oval, subterminal.

Cultural characters: Strict anaerobes grow on simple media.

Resistance:

· Spores of the organism are highly resistant to heat, withstanding 100 0 C for at last 3-5 hours.

BOTULISM

Pathogenesis:

· Botulism is not an infection. It is an intoxication resulting from the ingestion of preformed toxin of Cl. botulinium in food.

· The most common offenders are spiced, smoked, vacuum packed or canned alkaline foods that are eaten without cooking. In such foods, under anaerobic conditions spores of Cl. botulinium germinate and produce toxin.

· The toxin blocks the release of acetylcholine leading to flaccid paralysis.

· Death results from respiratory or cardiac failure. There is no diarrhea, vomiting or fever.

Diagnosis:

1. The toxin can be detected by passive haemagglutination or RIA in patient’s serum or food remnants.

2. The toxin can be demonstrated in patient’s serum or food remnants by injection into mice, which will die with generalized flaccid paralysis,

Treatment:

· Trivalent antitoxin (A, B, and E) is given with respiratory support.

· Metronidazole or penicillin may be used.

Prevention:

· Careful sterilization of food before canning.

· Spore germination in foods prevented by monitoring foods in an acid pH, by high sugar content or storing the foods at 40 C.

· Swollen cans should be discarded.

· Antitoxin should be given to suspected cases.

· Active immunity (toxoid) should be given to laboratories staff.

Clostridium difficile

· The organism is carried in the GIT.

· It causes pseudomembranous colitis and antibiotic associated diarrhea and is the commonest cause of hospital acquired diarrhea. These conditions occur as a complication of antibiotic therapy as ampicillin, clindamycin and some cephalosporins. . .

Treatment:

· Withdraw the causative antibiotic.

· Treat with metronidazole or vancomycin and replacement fluids.

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