Corynebacterium�Diphtheria

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Prof.

Zainab A. Aldhaher

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Corynebacterium

• Gram + Non Acid fast, Non motile,
• Irregularly stained with granules,
• Club shaped swelling at one or both ends so the name
• Important Pathogen

Corynebacterium diphtheria, Diptheros meaning leather,

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It’s a localized infectious disease, which usually attacks the throat and nose mucous membrane

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• C. diphtheriae is an aerobic gram-positive bacillus.
• Pleomorphic, club-end
• Non-spore-forming
• Non-acid-fast
• Non-motile

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Definition

• Diphtheria is an acute infectious disease that typically strikes the upper respiratory tract including the throat. It is caused by infection with the bacteria Corynebacterium diphtheria. It’s characterized by sore throat and mild fever at first. As the disease progresses, a membranous substance forms in the throat that makes it difficult to breathe and swallow.

Causes,,,,

• Corynebacterium diphtheriae causes diphtheria. Usually the bacteria multiply on or near the surface of the mucous membranes of the throat, where they cause inflammation.

• The inflammation may spread to the voice box (larynx) and may make your throat swell, narrowing your airway. Disease-causing strains of C. diphtheriae release a damaging substance (toxin), which can also involve the heart, brain and nerves.

• Pathogenesis
• C. diphtheria infects the respiratory tract by droplet inhalation or infects the skin by direct contact.
• Most clinical infections are contracted from carriers rather than symptomatic patients.
• C. diphtheria carriers usually harbor the organism in their throat or nose.

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• The organism doesn’t penetrate deeply into mucosal tissue and bacteremia doesn’t occur
• The organism starts to multiply at the site of entry and produces small amount of exotoxin to kill any phatocytic cell and then multiplies freely causing inflammation of the throat with local necrosis
• At the same time the organism secretes exotoxin to the blood

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Diphtheria Exotoxin

• It is a heat labile polypeptide composed of two fragments : A (active) and B (binding)
• Virulence is due to an extoxin
• It inhibits protein synthesis – kills cells
• Causes necrosis (death) of cells in upper respiratory tract – Pseudomembrane formation
• Toxin can be distributed systemically to cause life – threatening damage to organs

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Signs and symptoms

• A sore throat
• Painful swallowing
• Swollen glands (enlarged lymph nodes) in your neck
• Signs and symptoms usually begin two to five days after a person becomes infected.

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• A thick, gray membrane covering your throat and tonsils
• Difficulty breathing or rapid breathing
• Nasal discharge
• Fever and chills

Etiology

• There are three biotypes — gravis, Intermedius, and mitis. The most severe clinical type of this disease is associated with the gravis biotype, but any strain may produce toxin.

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Staining methods

• Grams method
• Albert's stain
• Neissers stain
• Ponders stain
• On staining seen as Pairs, Appear as v and L letters, resembling Chinese letter pattern or also called cuneiform arrangement.

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Cultural characters

• Need enrichment Media
• Contain
• Blood, Serum or Egg 37 ᵒc ph 7.4
• Aerobic/Facultative anaerobic.
• Commonly used medium
• Loeffler serum slope,
• Tellurite Blood agar

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Gram +ve Bacilli and Colonies

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Culturing

• Selective & differential medium
• Corynebacterium are resistant to tellurite
• Reduced to tellurium
• Forms deposit in colonies
• Colonies appear dark
• Biotypes
• gravis, Intermedius, mitis

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Growing on Culture Plates

• Loffler serum slope

Grows rapidly in 6 -8 hours, Small white opaque disks Turns to yellow

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Commonly used medium�

• Tellurite blood agar Contains tellurite 0.04 tellurite Inhibits other bacteria
• Produce Grey/Black colonies.

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Thick Membrane

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Pseudo membrane

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Laboratory Diagnosis

• Specific treatment is more important than Laboratory Diagnosis.
• Isolation of Diphtheria bacilli.
• Testing for toxigenicity
• Tissue culture test
• Polymerase chain reaction
• Elisa test

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Collection of Specimens

1. Throat swabs for

Smear examinations

1. Gram s staining,
2. Albert's, Ponders
2. Immunoflorescent methods
3. Cultures on :
1. Loeffers serum slope
2. Tellurite Blood agar,
3. Blood agar.

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Isolation of C.diptheria

• Serum slope – Growth in 6 – 8 hours,
• Stain with Neissers stain Albert's stain
• Bacilli have metachromatic granules,
• Tellurite Blood agar takes two days for manifestation of colonies,

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Toxigenicity Tests

In Vitro Elek test

low [Fe 2+] induces toxin

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Schick Test ( Out dated )

Schick test: It is an intradermal test, the test is carried out by injecting intradermally into the skin of forearm 0.2 ml of diphtheria toxin, while into the opposite arm is injected as a control, the same amount of toxin which has been inactivated by heat.

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Interpretation

• Negative reaction: If a person had immunity to diphtheria, no reaction will be observed on either arm.
• Positive reaction: An area of in duration 10-15 mm in diameter generally appears within 24-36 hours reaching its maximum development by 4-7 days, the control arm shows no change. The person is susceptible to diphtheria.
• False positive reaction: A red flush develops in both arms, the reaction fades very quickly, and disappears by 4^th day. This is an allergic type of reaction found in certain individuals
• Combined reaction: the control arm shows pseudo positive reaction and the test arm is true +ve reaction, susceptible and need vaccination

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Schick Test

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Prevention�

Vaccination: Immunisation with diphtheria toxoid, combined with tetanus and pertussis toxoid (DTP vaccine), should be given to all children at two, three and four months of age. Booster doses are given between the ages of 3 and 5 years.

The child is given a further booster vaccine before leaving school and is then considered to be protected for a further 10 years (16 – 18 years).

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Passive Immunization

• Given in Acute infections
• Give Subcutaneously
• 500 – 1000 Units of Antitoxin
• Given as Horse Serum
• Combined in Acute Infections ( Both Active Immunization with Toxoid and Antitoxin.

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Treatment

• Commonly used antibiotics,
• Penicillin parentally,
• Oral Erythromycin

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