Cornynebacteriaceae (Murray 3rd Ed pp 213)

Have a cell wall containing: arabinose, galactose, meso-diaminopimelic acid, short chain mycolic acids. Gram stain (gram +ve) resemble clumps of “chinese letters”. Metachromatic granules may be seen with special staining. They are aerobic + facultative anaerobes, non-motile, catalase positive, ferment carbohydrates ≫ lactic acid.

Pathogenesis (Murray 3^rd Ed pp 213)

The toxicity of C. Diphtheriae is attributed to the exotoxin produced. Before being secreted by the bacteria, the leader sequence of the exotoxin must be cleaved, and the protein is broken up into two subunits connected to each other by a disulfide bond. Three regions exist on this molecule: receptor binding region, translocation region, catalytic region. The receptor region binds to receptors on human cells (receptors particularly present on heart and nerve cells), it is engulfed (endocytosis), A subunit enters the cytoplasm (mediated by translocation region of B subunit). A subunit breaks down factor required for protein synthesis. Therefore protein synthesis is terminated.

Disease (Murray 3^rd Ed pp 214)

Upper Respiratory Tract infections can be caused: bacterial multiplication on the epithelial cells of the pharynx causing malaise, sore throat, pharyngitis, fever. Exudate becomes thick pseudomembrane forming over pharynx, can extend up to nasal cavity, larynx, tonsils and uvula. Firm adhesion of membrane means difficulty in dislodging. Cutaneous diphtheria occurs when bacteria enter subcutaneous tissue due to break in the skin, causing chronic ulceration.

Diagnosis (Murray 3^rd Ed pp 214)

Microscopic evaluation is not diagnostic, although metachromatic granules may be present with methylene stains. Specimens should be isolated from nasopharynx, throat and the inoculated on non-selective laboratory media, as well as selective media (i.e.: cysteine-tellurite, Loffler’s medium). Biochemical tests should be done for confirmation. All specimens should be tested for toxicity. Inject antitoxin and check for neutralisation.

Treatment, Prevention, Control (Murray 3^rd Ed pp 215)

Administer anti-toxin before host cell engulfs it. Penicillin is used to eliminate C. diphtheriae, terminating toxin production. Patients should be isolated, minimal contact with 2^nd persons. Active immunisation ≫ prevention. Booster doses every 10 years throughout life. Schick test is used to determine if antibodies to diphtheria are present

Have a cell wall containing: arabinose, galactose, meso-diaminopimelic acid, short chain mycolic acids. Gram stain (gram +ve) resemble clumps of “chinese letters”. Metachromatic granules may be seen with special staining. They are aerobic + facultative anaerobes, non-motile, catalase positive, ferment carbohydrates ≫ lactic acid.

Pathogenesis (Murray 3^rd Ed pp 213)

The toxicity of C. Diphtheriae is attributed to the exotoxin produced. Before being secreted by the bacteria, the leader sequence of the exotoxin must be cleaved, and the protein is broken up into two subunits connected to each other by a disulfide bond. Three regions exist on this molecule: receptor binding region, translocation region, catalytic region. The receptor region binds to receptors on human cells (receptors particularly present on heart and nerve cells), it is engulfed (endocytosis), A subunit enters the cytoplasm (mediated by translocation region of B subunit). A subunit breaks down factor required for protein synthesis. Therefore protein synthesis is terminated.

Disease (Murray 3^rd Ed pp 214)

Upper Respiratory Tract infections can be caused: bacterial multiplication on the epithelial cells of the pharynx causing malaise, sore throat, pharyngitis, fever. Exudate becomes thick pseudomembrane forming over pharynx, can extend up to nasal cavity, larynx, tonsils and uvula. Firm adhesion of membrane means difficulty in dislodging. Cutaneous diphtheria occurs when bacteria enter subcutaneous tissue due to break in the skin, causing chronic ulceration.

Diagnosis (Murray 3^rd Ed pp 214)

Microscopic evaluation is not diagnostic, although metachromatic granules may be present with methylene stains. Specimens should be isolated from nasopharynx, throat and the inoculated on non-selective laboratory media, as well as selective media (i.e.: cysteine-tellurite, Loffler’s medium). Biochemical tests should be done for confirmation. All specimens should be tested for toxicity. Inject antitoxin and check for neutralisation.

Treatment, Prevention, Control (Murray 3^rd Ed pp 215)

Administer anti-toxin before host cell engulfs it. Penicillin is used to eliminate C. diphtheriae, terminating toxin production. Patients should be isolated, minimal contact with 2^nd persons. Active immunisation ≫ prevention. Booster doses every 10 years throughout life. Schick test is used to determine if antibodies to diphtheria are present ≫ introduce diphtheria toxin ≫ check for cell necrosis in skin, if +ve ≫ no antibodies present, if –ve ≫ antibodies present.

introduce diphtheria toxin ≫ check for cell necrosis in skin, if +ve ≫ no antibodies present, if –ve ≫ antibodies present.

Category: Microbiology Notes