Corynebacterium Diptheriae | Diphtheria | Osmosis

Summary

Corynebacterium diphtheriae, a gram-positive, club-shaped bacterium, causes diphtheria, an infection characterized by a leathery membrane in the throat. This bacteria has four subspecies, with some producing the diphtheria toxin (DT) after being infected by a beta bacteriophage. DT disrupts protein synthesis, leading to cell death and damage to organs like the heart, kidneys, and nerves. Diphtheria spreads via respiratory droplets and can cause symptoms like a sore throat, swollen neck, and difficulty breathing. Diagnosis involves bacterial cultures and toxin detection, and treatment includes antibiotics and diphtheria antitoxin. Vaccination with DTaP prevents the disease.

Takeaways

• 😀 Corynebacterium diphtheriae is a gram-positive, club-shaped bacterium that causes diphtheria, an infection with a leathery membrane in the throat.
• 😀 The bacteria has four main subspecies: *C. diphtheriae* mitis, *C. diphtheriae* intermedius, *C. diphtheriae* gravis, and *C. diphtheriae* belfanti.
• 😀 It is an aerobic, non-spore-forming bacteria that takes up purple dye when gram-stained, indicating it is gram-positive.
• 😀 *C. diphtheriae* produces metachromatic granules that appear as dark blue dots when stained with Albert stain.
• 😀 The bacteria can form a characteristic 'Chinese letter' pattern under the microscope when stained.
• 😀 *C. diphtheriae* is fastidious, requiring special enriched media like cysteine tellurite blood agar to grow, forming black colonies.
• 😀 *C. diphtheriae* becomes toxigenic when infected by a beta bacteriophage, producing diphtheria toxin (DT), which can damage host cells.
• 😀 Diphtheria toxin (DT) consists of two subunits: A and B. The B subunit binds to host cells, and the A subunit interferes with protein synthesis, causing cell death.
• 😀 Diphtheria spreads through respiratory droplets, often causing pharyngeal diphtheria but can also cause cutaneous diphtheria through skin lesions.
• 😀 Symptoms of diphtheria include a sore throat, difficulty breathing, swollen neck (Bull neck), and a gray adherent membrane in the throat, which can block the airways.
• 😀 If untreated, diphtheria can lead to complications like myocarditis, kidney damage, polyneuropathy, and nerve demyelination, especially in unvaccinated or immunocompromised individuals.
• 😀 Diagnosis is typically done through bacterial cultures, and the strain’s toxigenicity is tested with the Elek test or PCR for the toxin gene.
• 😀 Treatment begins with isolating the patient and administering penicillin or erythromycin, along with diphtheria antitoxin for toxigenic strains.
• 😀 Vaccination with the DTaP vaccine (against diphtheria, tetanus, and pertussis) is crucial for prevention, usually administered in childhood.
• 😀 Diphtheria primarily affects unvaccinated individuals and can lead to severe complications if left untreated, emphasizing the importance of early diagnosis and treatment.

Q & A

What is the scientific name of the bacteria that causes diphtheria?

The scientific name of the bacteria that causes diphtheria is *Corynebacterium diphtheriae*, often referred to as C. diphtheriae.

What does the name *Corynebacterium* mean, and how does it relate to the bacteria's shape?

*Corynebacterium* comes from the Greek word 'koryne', meaning 'club', which refers to the club-shaped appearance of the bacteria.

What are the four subspecies of *Corynebacterium diphtheriae*?

The four subspecies of *Corynebacterium diphtheriae* are *C. diphtheriae* diphtheriae (C diph3a), *C. diphtheriae* intermedius, *C. diphtheriae* gravis, and *C. diphtheriae* belfonte.

How is *Corynebacterium diphtheriae* identified when stained in a laboratory?

When stained with Albert stain, *Corynebacterium diphtheriae* appears as green, club-shaped bacteria with metachromatic granules, which are dark blue dots made of phosphate located at the bacterial poles.

What does it mean that *Corynebacterium diphtheriae* is a 'fastidious' bacteria?

Being 'fastidious' means that *Corynebacterium diphtheriae* requires special nutrients and enriched media to grow. It cannot grow on standard laboratory media.

What is the role of diphtheria toxin (DT) in the infection process?

Diphtheria toxin (DT) is a cytotoxic protein that damages host cells. It binds to host cell membranes and interferes with protein synthesis by ADP ribosylation of the elongation factor EF2, leading to cell death.

What is the significance of beta bacteriophages in *Corynebacterium diphtheriae* infections?

Beta bacteriophages are viruses that can infect *Corynebacterium diphtheriae*, causing it to become toxogenic. This means the bacteria starts producing diphtheria toxin, which causes tissue damage and inflammation.

What are the potential severe complications of untreated diphtheria?

Untreated diphtheria can lead to severe complications such as myocarditis (heart inflammation), acute tubular necrosis (kidney damage), polyneuropathy (nerve damage), and even death due to asphyxiation from airway obstruction.

How is diphtheria diagnosed?

Diphtheria is diagnosed by culturing swabs from the pharynx or suspected skin lesions to isolate *Corynebacterium diphtheriae*. Toxogenic strains are identified using the Elek test or PCR to detect the presence of diphtheria toxin-producing genes.

What is the recommended treatment for diphtheria?

The treatment for diphtheria starts with isolation and antibiotics like penicillin G or erythromycin. If the strain is toxogenic, diphtheria antitoxin is administered to neutralize the diphtheria toxin.

How can diphtheria be prevented?

Diphtheria can be prevented with a vaccine containing a toxoid of the diphtheria toxin. This is usually combined with vaccines for tetanus and pertussis, forming the DTaP vaccine, given to children between two months and six years of age.