محاضره Clostridium

Genus: Clostridium
Characteristics:
• Clostridia are anaerobic, spore-forming motile, gram-positive Rods
• Most species are soil saprophytes but a few are pathogens to human.
• They inhabit human and animal intestine, soil, water, decaying animal and plant matter
• Spores of clostridia are wider than the diameter of organism and located centrally,
subterminally and terminally
• Species of medical importance:
C. perfringens
C. tetani
C. botulinum
C.difficile

Clostridium perfringens
Characteristics:
• Capsulated, non-motile, short gram-positive rods in which spores are hardly seen.
• there are five toxigenic groups : A-E
• Human disease is caused by C. perfringens type A and C Pathogenicity determinant:
1. Enzymes: Digest collagen of subcutaneous tissue and muscle.
. Collagenase
. Proteinase
. Hyaluronidase
. Dnase
2. Toxins
. PhospholipaseC (? toxin)
It has lethal, necrotizing and hemolytic effect on tissue. It causes cell lysis due to lecithinase action on the lecithin which is found in mammalian cell membrane.
. Theta toxin
It has hemolytic and necrotic effect on tissue.
. Enterotoxin
Clinical manifestation:
1. Clostridial myonecrosis: Gas gangrene . IP(Incubation period) =1-3 days Colonization of devitalized tramatized wound by C.perfringens spores, and organism germiation and release of toxins Presentation: Muscle and subcutaneous tissue necrosiss and crepitation Foul smelling wound discharge Fever, toxaemia, hemolytic anemia, Shock
2. Clostridial food poisoning It causes secretory diarrhea due to release of enterotoxin in theIntestine Self-limiting diarrhea similar to that produced by B. cereus

Laboratory diagnosis:
Specimen: Infected tissue, pus, vomitus, left-over food, serum
Smear: Non-motile, capsulated, thick brick-shaped gram positive rods in smears from tissue; spores are rarely seen.
Culture:
1. Blood agar medium
. ?-hemolytic colonies are seen in blood agar in anaerobic atmosphere.
. Some strains produce double zone of hemolysis.
2. Cooked meat medium(Chopped meat-glucose medium)
Thioglycolate medium
. Saccharolytic property showing reddening of the meat with a rancid smell due to carbohydrate decomposition.
. Proteolytic property showing blackening of the meat with unpleasant smell due to protein decomposition.
. Formation of gas
Biochemical reaction:
. Nagler reaction: Lecithinase C activity- Opacity in the egg-yolk medium due to lecithin break down
Procedure:
1. Streak colonies of C. perfringens on egg-yolk agar.
2. Cover half of the medium with C. perfringens antitoxin.
3. Look for dense opacity production by the growth of C. perfringens; but no opacity on the area with antitoxin.
. Lactose fermentation: Reddening of the medium; red colonies when exposed to air.
. Litmus milk medium: “stormy- clot” formation due to acid and gas formation.
Identification of C.perfringens rests on colony form, hemolysis pattern, biochemical reaction, and toxin production and neutralization by specific antisera.

Treatment:
Penicillin Prompt and extensive wound debridement Polyvalent antitoxin Prevention and control Early adequate contaminated wound cleansing and debridement

Closridium difficile
General characteristics:
. Not frequently found in the healthy adult, but is found often in the hospital environment
. Produce cytotoxins ( A and B)
. Human feces are the expected source of the organism

Pathogenesis and clinical features:
Administration of antibiotics like ampicillin, clindamycin and cephalosporins results in killing of colonic normal flora and proliferation of drug resistant C.difficile and release of cytoxins
Clinically presents with pseudomembraneous colitis and manifests with fever, abdominal cramps, watery or bloody diarrhea leading to dehydration, septicemia and shock

Lab. Dignosis: Identification of toxin A and B in feces by latex agglutination test
Treatment: Discontinuation of offending drugs Administration of metronidazole or vancomycin

Clostridium tetani
General characteristics:
• Worldwide in distribution in the soil and in animal feces
• Longer and thinner gram-positive rods with round terminal spores giving characteristic “drum-stick” appearance.
• There are ten antigenic types of c. tetani but all produce the same neurotoxin.
• The toxin has two components:
1. Tetanospasmin: Neurotoxic property
2. Tetanolysin: Hemolytic property

Pathogenesis and Clinical manifestation:
Infection of devitalized tissue (wound, burn, injury, umblical stamp, surgical suture) by spores of C.tetani ? Germination of the spore and development of vegetative organism? Neurotoxin release from vegetative cells ? The toxin binds to receptors on the presynaptic membrane of motor neuron the retrograde axonal transport to the spinalcord and brain stem ? Inhibition of inhibitory glycinergic and GABAergic secreting neurons ? Spatic paralysis, muscle spasms and hyperreflexia
IP= 4-5 days to several wks
Tetanus classical presentation:
. Lock jaw or trismus
. Arched back or opistotonus
. Arm flexion and of leg extension
. Fever and sweating
. Muscle spasm and rigidity
Laboratory diagnosis: The bacteria can be cultured in a media with anaerobic atmosphere. Proof of isolation of C.tetani must rest on production of toxin and its neutralization by specific antitoxin
Diagnosis is exclusively by clinical picture and history of injury
Treatment:
Administration of penicillin
Proper wound debridement
Provision of tetanus antitoxin (TAT)
Prevention and control:
Avoid traditional application of mud or ash over the umbilical stump
Proper wound handling
Immunization with tetanus toxoid
NB: Since treatment of tetanus is not satisfactory, prevention is all important

Clostridium botulinum
General characteristics:
• Spores of C. botulinum are widely distributed in soil, they often contaminate vegetables, fruits and other materials.
• Produce a neurotoxin which is the most active known poison, and considered to be the major agent of bioterrorism and biologic warfare
There are seven serotypes(A-G) of which A,B and E are the principal causes of human illness.
Pathogenesis and Clinical manifestation:
1. Food botulism
. IP = 18-24 hrs
. Route of entry is under cooked consumption of C. botulinum toxin contaminated spiced, smoked, vaccumpacked or canned food
.The toxin is absorbed from the gut and acts by blocking the release of acetylcholine at synapses and neuromuscularjunction and manifests with flaccid paralysis and visual disturbance, inability to swallow, and speech difficulty Death is secondary to respiratory failure or cardiac arrest
2. Infantile botulism
C.botulinum type A or B is usually implicated and affects infants when mixed feeding starts (after fourth month of life).
Ingestion and colonisation of the gut with C.botulinum, and production of toxin and adsorption of toxin leads to poor feeding, paralysis (floppy baby), and cranial nerve palsy.
Diagnosed by demonstration of the organism or toxin from the stool
3. WC.botulinum type A is usually implicated and caused by the production of toxin by C.botulinum in wounds.The symptoms are the same as those in food poisonig.ound botulism

Laboratory diagnosis:
.Demonstration of toxin in patient’s serum and left over food.
. Death of mice after intra-peritoneal injection of toxin.
Treatment:
Administration of intravenous trivalent antitoxin ( A,B,E)
Mechanical ventilator for respiratory support

Prevention and control:
. Sufficient heating of cannaed foods before consumption
. Strict regularion of commercial canning
. Pr