An acid-fast stain (either Ziehl–Neelsen, or Kinyoun’s Cold Acid-Fast [an easy one to do in-house]) would differentiate the two species; Nocardia species are partially acid-fast, whilst Actinomyces are acid-fast negative. | An acid-fast stain (either Ziehl–Neelsen, or Kinyoun’s Cold Acid-Fast [an easy one to do in-house]) would differentiate the two species; Nocardia species are partially acid-fast, whilst Actinomyces are acid-fast negative. |