Microbiology
Summary
Nocardia asteroides is an obligate aerobic, gram-positive branching rod primarily found in soil. It stains weakly acid-fast due to the presence of mycolic acids in its cell wall. Notably, Nocardia is catalase-positive and urease-positive.
Nocardia primarily affects immunocompromised patients, especially those with impaired cell-mediated immunity. This includes patients with HIV, transplant patients, and those taking glucocorticoids. There are three main sites of infection: pulmonary, CNS, and cutaneous. Pulmonary nocardiosis typically manifests as pneumonia with lung abscess formation. Nocardia can also disseminate, leading to brain abscesses due to its affinity for neural tissue. Finally, cutaneous nocardiosis can occur when open wounds are exposed to dirt, resulting in a pyogenic response with the production of indurated lesions. The standard therapy for nocardiosis is sulfonamides like TMP-SMX.
Lesson Outline
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FAQs
N. asteroides is a gram-positive, obligate aerobic branching rod that is found in soil and water. It is acid-fast and catalase-positive. It is significant in clinical settings because it can cause pulmonary nocardiosis, particularly in immunocompromised individuals. Treatment often includes the use of sulfonamides.
Nocardia species can be identified by their filamentous, branching morphology and their ability to form "fragmented hyphae." These weakly acid-fast bacteria retain the carbolfuchsin stain after acid washing due to mycolic acids in their cell walls. They require oxygen for growth, are catalase-positive, and urease-positive, further assisting in their differentiation from other bacteria.
Pulmonary nocardiosis is an infection of the lungs caused by Nocardia bacteria. The bacteria can enter the respiratory system through inhalation of contaminated dust particles from soil. Immunocompromised individuals are more susceptible to this infection, which can lead to symptoms such as cough, fever, chest pain, and difficulty breathing. If left untreated, pulmonary nocardiosis can potentially cause severe complications, such as lung abscesses and dissemination to other organs.
The recommended treatment for infections caused by Nocardia is the use of sulfonamides, such as trimethoprim-sulfamethoxazole. However, due to potential resistance, susceptibility testing is recommended for optimal therapy. In severe cases or when a patient cannot tolerate sulfonamide therapy, alternative treatments such as amikacin, imipenem, or linezolid may be considered under the supervision of a healthcare provider.
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