Nocardia

They resemble Actinomyces morphologically being Gram positive, branching filaments. They can be differentiated from Actinomyces as Nocardia are weakly acid fast while Actinomyces are not acid fast. They are strict aerobes causing pneumonia and subcutaneous granulomas called mycetomas.

The lung infection can present as a miliary pneumonia, lung abscess, nodule or empyema which may disseminate systemically. Samples are pus, sputum, granules which can be Gram stained to show typical morphology and will be weakly acid fast with a dilute solution of HCl or dilute 1% sulphuric acid. Unlike Actinomyces, Nocardia will grow aerobically to form dry, wrinkled colonies.