Corynebacterium Actinomyces Other Gram Positive Rod Bacteria

■ Diphtheria bacteria are pleomorphic, club-shaped rod bacteria that often have polar bodies and group in V, Y, or palisade forms. They can be grown on enriched nutrient media. Their pathogenicity derives from diphtheria toxin, which binds to receptors of sensitive cells with the B fragment. Once the binding process is completed, the active A fragment invades the cell. This substance irreversibly blocks translation in the protein biosynthesis chain. The toxin gene is a component of the b prophage. Local and systemic intoxications are differentiated when evaluating the clinical picture. Local infection usually affects the tonsils, on which the diphtherial pseudomembrane develops. Systemic intoxications affect mainly the liver, kidneys, adrenal glands, cardiac muscle, and cranial nerves. Laboratory diagnosis is based on pathogen identification. The most important treatment is antitoxin therapy. Diphtheria occurs only in humans. Thanks to extensive diphtheria toxoid vaccination programs, it is now rare.

Actinomycetes are part of the normal mucosal flora. These are Gram-positive rods that often occur in the form of branched filaments in young cultures. Conglomerates of microcolonies in pus form so-called sulfur granules. Actinomycetes are obligate anaerobes. The pathogens enter body tissues through mucosa defects. Monoinfections are rare, the most frequent case being actinomycetes-dominated endogenous polyinfections. Cervicofacial actinomycosis, caused by oral cavity colonizer A. israelii, is the most frequent form of actinomycosis. Treatment includes surgical procedures and antibiosis with aminopenicillins. ■

The group of Gram-positive, irregular (pleomorphic), nonsporing rod bacteria includes many different genera that are normal components of the skin and mucosal flora (Table 4.3, p. 261). Pathogens in this group cause two characteristic diseases: diphtheria, caused by Corynebacterium diphtheriae and actinomycosis, caused mainly by Actinomyces israelii.

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