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Acid-fast bodies in faecal smears stained by the modified Ziehl-Neelsen technique
1Scottish Meningococcus and Pneumococcus Reference Laboratory, Department of Microbiology, House on the Hill, Stobhill Hospital, Glasgow G21 3UW, UK.
Abstract:
The modified Ziehl-Neelsen (ZN) stain has proved useful in the laboratory diagnosis of cryptosporidiosis and, more recently, for the laboratory diagnosis of cyclospora. Apart from cryptosporidia and cyclospora, many other organisms and artefacts are present in faeces, and may be seen in faecal smears stained by the modified ZN method. Described here is the presence of such organisms and artefacts in faecal samples submitted to the routine microbiology laboratory of a district general hospital. Over 6000 faecal smears were examined using the modified ZN method, with an incidence of cyclospora and cryptosporidium of approximately 0.1% and 1%, respectively. Other organisms and artefacts were observed, with an incidence ranging from 0.1% to 1%. It is emphasised that the identification of known gastrointestinal tract pathogens should not rely solely on the results of their staining reactions. It is essential that criteria such as morphology and size be taken into account to differentiate organisms with similar staining reactions.
Insights
The modified Ziehl-Neelsen stain aids in diagnosing cryptosporidiosis and cyclosporiasis. Careful examination of morphology and size is crucial for accurate identification of gastrointestinal pathogens beyond just staining reactions.
Area of Science:
- Medical Microbiology
- Diagnostic Parasitology
Background:
- The modified Ziehl-Neelsen (ZN) stain is a valuable laboratory tool for diagnosing parasitic infections.
- Its utility extends to identifying Cryptosporidium and Cyclospora in fecal samples.
- Fecal smears stained with modified ZN may reveal various organisms and artifacts beyond target pathogens.
Purpose of the Study:
- To document the range of organisms and artifacts observed in routine fecal smears stained by the modified ZN method.
- To assess the incidence of Cyclospora and Cryptosporidium in a district general hospital's microbiology laboratory.
- To highlight the importance of morphological criteria in identifying gastrointestinal pathogens.
Main Methods:
- Examination of over 6000 fecal smears using the modified Ziehl-Neelsen staining technique.
- Systematic recording of observed organisms and artifacts.
- Incidence calculation for Cyclospora, Cryptosporidium, and other identified entities.
Main Results:
- The modified ZN stain identified Cyclospora with an approximate incidence of 0.1% and Cryptosporidium with approximately 1%.
- A variety of other organisms and artifacts were observed, with incidences ranging from 0.1% to 1%.
- The study confirmed the presence of non-pathogenic or incidental findings alongside target parasites.
Conclusions:
- The modified ZN stain is effective for detecting Cryptosporidium and Cyclospora but also reveals other fecal contents.
- Accurate identification of gastrointestinal pathogens requires consideration of morphology and size, not solely staining characteristics.
- Relying exclusively on staining reactions can lead to misidentification; comprehensive morphological assessment is essential.