The organism that exhibits characteristic end-over-end tumbling motility when incubated in nutrient ...

A
L. monocytogenes can be presumptively identified by observation of motility by direct wet mount. The organism exhibits characteristic end-over-end tumbling motility when incubated in nutrient broth at room temperature for 1 to 2 hours.

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D
The only organisms that are partially acid-fast positive and acid-fast negative are Nocardia and Streptomyces, respectively. All other combinations are either both acid-fast positive (Nocardia and Rhodococcus) or both acid-fast negative (Streptomyces and Actinomadura; Dermatophilus and Nocardiopsis).

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D
Nocardia spp. cause three types of skin infections in individuals who are immunocompromised: (1) mycetoma, which is a chronic, localized, painless, subcutaneous infection; (2) lymphocuta-neous infections; and (3) skin abscesses or cellulites. In individuals who are immunocompromised, Nocardia spp. can cause invasive pulmonary infections and disseminated infections.

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A
Rhodococcus equi has been the organism most commonly associated with human disease, partic-ularly in patients who are immunocompromised, such as those infected with HIV. R. equi is a facultative intracellular organism that can persist and replicate within macrophages. Determinants of virulence of R. equi are under investigation and may involve cell wall mycolic acids that play a role in intracellular survival, production of interleukin 4, and granuloma formation.

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A
Gardnerella are small pleomorphic gram-variable or gram-negative coccobacilli and have short rods. The wet mount and Gram stain of vaginal secretions are key tests for diagnosing bacterial vaginosis caused by G. vaginalis. A wet mount prepared in saline solution reveals the characte-ristic clue cells, which are large, squamous epithelial cells with numerous attached small rods. A Gram-stained smear of the discharge shows the attached organisms to be gram-variable coc-cobacilli. Clue cells typically are present, and large numbers of gram-positive rods (e.g., lactoba-cilli) representing normal vaginal flora are absent or few in number.

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