Cytology Q&A 02

This question was provided by Manson Publishing as part of the OVAL Project. See more Cytology Q&A.

A ten-year-old spayed female barn cat presented with severe dyspnoea and cyanosis. Thoracocentesis yielded a foul-smelling, purulent, grey material. A smear of the material was made (Gram’s, ×100 oil).

Question	Answer		Article
What are the structures arrowed?	There is a clump of filamentous gram-negative rods.		Link to Article
What are two organisms that have this kind of morphology?	Actinomyces species and Nocardia species are bacterial genera that have this morphology. Of the two, Actinomyces is most likely in cases of pyothorax in the cat.		Link to Article
How can you differentiate between the two before culture results can be received?	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.		Link to Article