Chapter 19: Gram-Positive Pathogens

These flashcards cover key concepts about Corynebacterium diphtheriae, its distinguishing features, virulence factors, transmission, and diagnostic methods.

What is the distinctive feature of Corynebacterium bacteria?

The presence of metachromatic granules.

What virulence factor does Corynebacterium diphtheriae possess that causes cell death?

Diphtheria toxin, which destroys elongation factor EF2 required for protein synthesis.

How is Corynebacterium diphtheriae primarily transmitted?

From person to person via respiratory droplets or skin contact.

What is the role of the Elek test in diagnosing diphtheria?

It is an immunodiffusion assay that detects the presence of the diphtheria toxin in a sample.

What is the distinctive feature of Corynebacterium bacteria?

The presence of metachromatic granules.

What virulence factor does Corynebacterium diphtheriae possess that causes cell death?

Diphtheria toxin, which destroys elongation factor EF2 required for protein synthesis.

How is Corynebacterium diphtheriae primarily transmitted?

From person to person via respiratory droplets or skin contact.

What is the role of the Elek test in diagnosing diphtheria?

It is an immunodiffusion assay that detects the presence of the diphtheria toxin in a sample.

What are the characteristic clinical presentations of diphtheria?

Sore throat, fever, and the formation of a tough, leathery pseudomembrane in the pharynx, which can lead to airway obstruction. Systemic complications like myocarditis and neuropathy can also occur.

What is the primary method for preventing diphtheria?

Vaccination with the DTP, DTaP, or Tdap vaccine, which contains diphtheria toxoid (inactivated diphtheria toxin).

How is diphtheria primarily treated?

Administration of diphtheria antitoxin (DAT) to neutralize circulating toxin, along with antibiotics (e.g., penicillin or erythromycin) to eliminate the bacteria.

What is the Gram stain characteristic and morphology of Corynebacterium diphtheriae?

Gram-positive rods that appear club-shaped or in 'V' or 'L' arrangements (palisades).

What specific enzyme activity does diphtheria toxin possess that leads to its pathogenic effect?

It is an ADP-ribosyltransferase, which adds an ADP-ribose group to elongation factor EF2.

What type of genetic element carries the gene for diphtheria toxin?

A lysogenic beta-prophage.

What is the most severe cardio complication associated with diphtheria?

Myocarditis (inflammation of the heart muscle).

Beyond the pharynx, what other tissues can develop a pseudomembrane?

Larynx, trachea, nose, and skin (cutaneous diphtheria).

Why are antibiotics necessary in diphtheria treatment even after antitoxin administration?

To eliminate the bacteria and prevent further toxin production and transmission, as antitoxin only neutralizes circulating toxin, not the bacteria itself.

What is the functional difference between diphtheria toxin (active form) and diphtheria toxoid (inactivated form)?

Diphtheria toxin is active and causes disease, while diphtheria toxoid is detoxified but retains antigenicity, used in vaccines to stimulate protective immunity.

What unique culture medium is often used to isolate Corynebacterium diphtheriae and detect metachromatic granules?

Loeffler's serum medium enhances metachromatic granule formation, and tellurite agar (e.g., Tinsdale agar) inhibits most other flora and produces characteristic dark colonies.

What is the incubation period for diphtheria?

Typically 2 to 5 days, but can range from 1 to 10 days.

What is the primary reservoir for Corynebacterium diphtheriae?

Always humans; there is no known animal reservoir.

Describe the composition of the diphtheria pseudomembrane.

It is a tough, grayish membrane composed of fibrin, dead epithelial cells, leukocytes, erythrocytes, and bacteria.

What is the mechanism by which the diphtheria pseudomembrane can be life-threatening?

It can extend into the larynx and trachea, causing severe airway obstruction and suffocation.

What are some neurological complications that can arise from diphtheria?

Palatal paralysis, oculomotor paralysis, pharyngeal paralysis leading to difficulty swallowing, and peripheral neuropathies.

From what source is diphtheria antitoxin (DAT) typically derived?

It is typically equine (horse) antitoxin, meaning it's derived from horses immunized with diphtheria toxoid.

What is the mechanism of action of diphtheria toxin on a cellular level?

It inhibits protein synthesis in eukaryotic cells by ADP-ribosylating and inactivating elongation factor EF2, which is essential for ribosomal translocation during protein elongation.

What is a 'bull neck' appearance, and when is it observed in diphtheria?

A severe swelling of the lymph nodes and soft tissues of the neck, indicative of severe pharyngeal and cervical diphtheria.

How does the Diphtheria vaccine provide protection?

It elicits an immune response to the diphtheria toxoid, producing antibodies that neutralize the diphtheria toxin if an infection occurs, preventing its entry into cells and subsequent damage.

What is the term for diphtheria affecting the skin, often presenting as chronic, non-healing ulcers?

Cutaneous diphtheria.

What is the distinctive feature of Corynebacterium bacteria?

The presence of metachromatic granules.

What virulence factor does Corynebacterium diphtheriae possess that causes cell death?

Diphtheria toxin, which destroys elongation factor EF2 required for protein synthesis.

How is Corynebacterium diphtheriae primarily transmitted?

From person to person via respiratory droplets or skin contact.

What is the role of the Elek test in diagnosing diphtheria?

It is an immunodiffusion assay that detects the presence of the diphtheria toxin in a sample.

What are the characteristic clinical presentations of diphtheria?

Sore throat, fever, and the formation of a tough, leathery pseudomembrane in the pharynx, which can lead to airway obstruction. Systemic complications like myocarditis and neuropathy can also occur.

What is the primary method for preventing diphtheria?

Vaccination with the DTP, DTaP, or Tdap vaccine, which contains diphtheria toxoid (inactivated diphtheria toxin).

How is diphtheria primarily treated?

Administration of diphtheria antitoxin (DAT) to neutralize circulating toxin, along with antibiotics (e.g., penicillin or erythromycin) to eliminate the bacteria.

What is the Gram stain characteristic and morphology of Corynebacterium diphtheriae?

Gram-positive rods that appear club-shaped or in 'V' or 'L' arrangements (palisades).

What specific enzyme activity does diphtheria toxin possess that leads to its pathogenic effect?

It is an ADP-ribosyltransferase, which adds an ADP-ribose group to elongation factor EF2.

What type of genetic element carries the gene for diphtheria toxin?

A lysogenic beta-prophage.

What is the most severe cardio complication associated with diphtheria?

Myocarditis (inflammation of the heart muscle).

Beyond the pharynx, what other tissues can develop a pseudomembrane?

Larynx, trachea, nose, and skin (cutaneous diphtheria).

Why are antibiotics necessary in diphtheria treatment even after antitoxin administration?

To eliminate the bacteria and prevent further toxin production and transmission, as antitoxin only neutralizes circulating toxin, not the bacteria itself.

What is the functional difference between diphtheria toxin (active form) and diphtheria toxoid (inactivated form)?

Diphtheria toxin is active and causes disease, while diphtheria toxoid is detoxified but retains antigenicity, used in vaccines to stimulate protective immunity.

What unique culture medium is often used to isolate Corynebacterium diphtheriae and detect metachromatic granules?

Loeffler's serum medium enhances metachromatic granule formation, and tellurite agar (e.g., Tinsdale agar) inhibits most other flora and produces characteristic dark colonies.

What is the incubation period for diphtheria?

Typically 2 to 5 days, but can range from 1 to 10 days.

What is the primary reservoir for Corynebacterium diphtheriae?

Always humans; there is no known animal reservoir.

Describe the composition of the diphtheria pseudomembrane.

It is a tough, grayish membrane composed of fibrin, dead epithelial cells, leukocytes, erythrocytes, and bacteria.

What is the mechanism by which the diphtheria pseudomembrane can be life-threatening?

It can extend into the larynx and trachea, causing severe airway obstruction and suffocation.

What are some neurological complications that can arise from diphtheria?

Palatal paralysis, oculomotor paralysis, pharyngeal paralysis leading to difficulty swallowing, and peripheral neuropathies.

From what source is diphtheria antitoxin (DAT) typically derived?

It is typically equine (horse) antitoxin, meaning it's derived from horses immunized with diphtheria toxoid.

What is the mechanism of action of diphtheria toxin on a cellular level?

It inhibits protein synthesis in eukaryotic cells by ADP-ribosylating and inactivating elongation factor EF2, which is essential for ribosomal translocation during protein elongation.

What is a 'bull neck' appearance, and when is it observed in diphtheria?

A severe swelling of the lymph nodes and soft tissues of the neck, indicative of severe pharyngeal and cervical diphtheria.

How does the Diphtheria vaccine provide protection?

It elicits an immune response to the diphtheria toxoid, producing antibodies that neutralize the diphtheria toxin if an infection occurs, preventing its entry into cells and subsequent damage.

What is the term for diphtheria affecting the skin, often presenting as chronic, non-healing ulcers?

Cutaneous diphtheria.

Besides C. diphtheriae, what other Corynebacterium species can rarely produce diphtheria toxin if infected with the diphtheria toxin gene?

Corynebacterium ulcerans and Corynebacterium pseudotuberculosis.

Describe the general structure of diphtheria toxin.

It is an A-B exotoxin composed of two subunits: an A (active) subunit and a B (binding/translocation) subunit. The B subunit binds to host cell receptors and mediates entry, while the A subunit carries the enzymatic activity.

How does diphtheria toxin enter host cells?

The B subunit binds to specific receptors (e.g., heparin-binding epidermal growth factor precursor) on the host cell surface, leading to endocytosis of the toxin. Inside the endosome, low pH causes a conformational change in the B subunit, facilitating the translocation of the A subunit into the host cell cytoplasm.

What environmental factor primarily regulates the production of diphtheria toxin by C. diphtheriae?

Low iron concentrations. Toxin production is repressed in the presence of high iron by the DtxR (diphtheria toxin repressor) protein.

What is the role of the DtxR protein in diphtheria toxin regulation?

DtxR is a bacterial regulatory protein that, when bound to iron, blocks the transcription of the diphtheria toxin gene, thereby preventing toxin production. In low-iron environments, DtxR does not bind iron, allowing toxin gene expression.

What unique staining characteristics do metachromatic granules exhibit with dyes like methylene blue?

They stain distinctly with methylene blue, appearing red-purple due to their polyphosphate composition, contrasting with the blue-stained cytoplasm.

What is the specific mechanism by which Diphtheria Antitoxin (DAT) provides therapeutic benefit?

DAT contains antibodies that bind to and neutralize free-circulating diphtheria toxin, preventing it from binding to and entering host cells. It does not affect toxin that has already entered cells.

Why is a throat or nasal swab culture crucial for the definitive diagnosis of diphtheria?

To isolate Corynebacterium diphtheriae and confirm its identity, and subsequently to perform toxin detection tests like the Elek test, as clinical symptoms can be mimicked by other pathogens.

How does diphtheria toxin reach distant organs like the heart and nerves to cause systemic complications?

The toxin produced locally in the pharynx (or other sites) can be absorbed into the bloodstream and circulate throughout the body, affecting susceptible cells in various organs, including the myocardium and peripheral nerves.

How long can an untreated diphtheria patient remain contagious?

Typically for 2 to 4 weeks, but sometimes longer, until the bacteria are eliminated from the pharynx. Antibiotic treatment significantly reduces the duration of contagiousness.