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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. |
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| 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. |
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| 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. |
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