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Pathology

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A 33- year old man presents with edematous right foot that has multiple draining sinuses. A Gram stain from one of these draining sinuses reveals gram-positive filamentous bacteria that are partially acid-fast. What is this organism? (AIIMS Nov 2014)



A Actinomyces israelii
B Corynebacterium diphtheriae

C Listeria monocytogenes
D Nocardia asteroids

Ans. D Nocardia asteroids

a. Nocardia (N. asteroides) and Actinomyces species are classified as filamentous soil bacteria, although they are often descanted among the fungi.

b. Israelii is a normal inhabitant of the mouth

c. it can be seen in the crypts of tonsillectomy specimens.

d. Actinomyces is a branched, filamentous gram-positive bacteria.

e. Two forms of disease produced by Actinomyces are cervicofacial actinomyces and pelvic actinomyces.

f. The former consists of an indurated (lumpy) jaw with multiple draining fistulas or abscesses.

g. Small yellow colonies called sulfur granules may be seen in the draining material.

h. Histologic section reveals tangled masses of gram-positive filamentous bacteria.

i. Cultures of Actinomyces grow as white masses with a domed surface, which is called a “molar tooth” appearance.

j. Another filamentous gram-positive bacteria is N. asteroides.

k. A characteristic that helps to differentiate these two is the fact that Nocardia is partially acid-fast.

l. Partial means using weak mineral acids in the acid- last stain.

m. Nocardia are aerobic and acid-fast, in contrast to Actinomyces species, which are strict anaerobes and not acid-fast.

Inhaled nocardial bacteria produce lung or skin infections.

a. Progressive pneumonia with purulent and abscesses is suggestive of nocardiosis, especially if dissemination to the brain or subcutaneous tissue occurs.

b. Nocardia is also one cause of mycetoma, a form of chronic inflammation of the skin that causes indurated abscesses with multiple draining sinuses.

c. Patients who develop nocardiosis are often immunosuppressed, and transplant rejection, steroid therapy, AIDS, or alveolar proteinosis are often antecedent.

d. Organisms in sputum, pus, or bronchial lavage specimens are gram-positive. A modified acid-fast stain should be used for diagnosis.

C. diphtheriae is a small, pleomorphic gram-positive bacillus that may have club-shaped swellings at either pole.

a. These rods tend to arrange themselves at right angles, producing characteristic V or Y configurations described as “Chinese characters.”

b. C. diphtheriae produces a toxin that blocks protein synthesis by causing irreversible inactivation of elongation factor 2 (EF-2).

c. This toxin can produce a pseudomembrane covering the larynx, which is difficult to peel away without causing bleeding, and heart damage with fatty change.

L. monocytogenes is a short, gram-positive, non- spore-forming bacillus that can produce neonatal disease or can result in stillbirth.

Characteristics that are unique to Listeria include a tumbling motility on hanging drop and an umbrella-shaped motility pattern when a specimen is stabbed into a test tube agar slant.

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