TAILIEUCHUNG - Chapter 131. Diphtheria and Other Infections Caused by Corynebacteria and Related Species

Diphtheria is a nasopharyngeal and skin infection caused by Corynebacterium diphtheriae. Toxigenic strains of C. diphtheriae produce a protein toxin that causes systemic toxicity, myocarditis, and polyneuropathy. The toxin is associated with the formation of pseudomembranes in the pharynx during respiratory diphtheria. While toxigenic strains most frequently cause pharyngeal diphtheria, nontoxigenic strains commonly cause cutaneous disease. In the United States and Europe, diphtheria has been controlled in recent years with effective vaccination, although sporadic outbreaks have occurred. Diphtheria is still common in the Caribbean, Latin America, and the Indian subcontinent, where mass immunization programs are not enforced. . | Chapter 131. Diphtheria and Other Infections Caused by Corynebacteria and Related Species Diphtheria is a nasopharyngeal and skin infection caused by Corynebacterium diphtheriae. Toxigenic strains of C. diphtheriae produce a protein toxin that causes systemic toxicity myocarditis and polyneuropathy. The toxin is associated with the formation of pseudomembranes in the pharynx during respiratory diphtheria. While toxigenic strains most frequently cause pharyngeal diphtheria nontoxigenic strains commonly cause cutaneous disease. In the United States and Europe diphtheria has been controlled in recent years with effective vaccination although sporadic outbreaks have occurred. Diphtheria is still common in the Caribbean Latin America and the Indian subcontinent where mass immunization programs are not enforced. Large epidemics have occurred in the independent states formerly encompassed by the Soviet Union. Additional outbreaks have been reported in Algeria China and Ecuador. Etiology C. diphtheriae is a gram-positive unencapsulated nonmotile nonsporulating bacillus. C. diphtheriae organisms have a characteristic club-shaped bacillary appearance and typically form clusters of parallel rays palisades that are referred to as Chinese characters. In the specific laboratory media recommended for the cultivation of C. diphtheriae tellurite colistin or nalidixic acid is responsible for selective isolation of the organism in the presence of other autochthonous pharyngeal microbes. Human isolates of C. diphtheriae may display nontoxigenic tox or toxigenic tox phenotypes. Corynebacteriophage beta carries the structural gene tox encoding diphtheria toxin and a family of closely related corynebacteriophages are responsible for toxigenic conversion of tox C. diphtheriae to the tox phenotype. Moreover lysogenic conversion from a nontoxigenic to a toxigenic phenotype has been shown to occur in situ. Growth of toxigenic strains of C. diphtheriae under iron-limiting conditions leads to

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