The primary difference between Nocardia and Actinomyces is that Nocardia is a genus of aerobic, filamentous, Gram-positive bacteria, while Actinomyces is a genus of anaerobic, Gram-positive bacteria.
Nocardia species are widely distributed in soil, water, and plant material, and can cause a range of infections in humans, including pneumonia, brain abscesses, and skin and soft tissue infections. Nocardia are typically not invasive, but can cause systemic disease, especially in immunocompromised individuals.
Actinomyces species are commensal bacteria of the oral cavity, and can cause a range of infections in humans, including endocarditis, abscesses, and periodontal disease. Actinomyces species are generally considered to be non-invasive but can cause systemic disease in immunocompromised individuals.
Another difference between Nocardia and Actinomyces is the type of antibiotics they are sensitive to. Nocardia are sensitive to sulfonamides and aminoglycosides, while Actinomyces are sensitive to penicillin, macrolides, and tetracycline.
Lastly, Nocardia species are Gram-positive and produce branching filaments, while Actinomyces species are Gram-positive and produce non-branching filaments.