Review Question - QID 101634

This child has a Corynebacterium diphtheriae infection. When C. diptheriae is cultured on Loeffler’s coagulated blood serum media and stained with an aniline dye, cytoplasmic metachromic (blue and red) granules are present.

C. diphtheriae causes diphtheria via a potent exotoxin that interferes with protein synthesis in cardiac and neural tissue. The bacteria colonizes the pharynx, where it forms a dark grey pseudomembrane composed of fibrin, leukocytes, epithelial cells, and C. diphtheriae cells. C. diphtheriae produces dark black, iridescent colonies on cysteine-tellurite agar. While most US children are given a DPT (Diphtheria, Pertussis, Tetanus) vaccine, the presence of pseudomembranous pharyngitis in a child should make clinicians suspicious of C. diphtheriae infection.

Pallerla et al. characterize granule formation in corynebacterium species; they conclude that metachromatic bodies, which are subcellular phosphate rich granules, exhibit a special color reaction when stained with basic dyes such as toluidine blue or Neisser stains. In order to obtain good visualization of these stained granules, cells are usually grown on specific media, such as Loeffler's blood serum media.

Ackerman reviews current immunization recommendations for adolescents, concluding that the Tdap vaccine, which includes tetanus and diphtheria toxoids as well as acellular pertussis vaccine, is recommended for adolescents 11 to 12 years of age as a booster to the DTap vaccine.

Illustration A depicts the metachromatic granules characteristic of C. diptheriae; this appearance is due to the staining of pockets of inorganic phosphate.
Illustration B depicts the black, iridescent appearance of C. diptheriae colonies grown on cysteine-tellurite agar.


Incorrect answers:
Answer 1: Serpentine growth patterns are characteristic of mycobacteria that produce cord factor, a virulent mycoside.
Answer 3: Lancet-shape is characteristic of Streptococcus pneumonia.
Answer 4: Long, branching filaments are characteristic of Nocardia and Actinomyces species.
Answer 5: Kidney-bean shaped diplococci are characteristic of Neisseria species.