Evaluation of faecal preservation and staining methods in the diagnosis of acute amoebiasis and giardiasis.

N Shetty, T Prabhu

Department of Microbiology, St John's Medical College, Bangalore, India.

The use of a faecal preservative and several staining methods, together with formalin ether concentration, were evaluated for the improved diagnosis of intestinal amoebiasis and giardiasis in 1285 patients with diarrhoea or dysentery and from asymptomatic controls. All samples were screened by three wet mount techniques. Thirty eight specimens of diarrhoeal or dysenteric stool were preserved in polyvinyl alcohol (PVA) and stained by trichrome and Spencer and Monroe short iron haematoxylin stain. Thirty nine preserved faecal samples submitted for routine screening were subjected to formalin ether concentration, wet mount examination, and permanent staining. Saline and buffered methylene blue (BMB) mounts were equally good for detection of trophozoite Entamoebae while Giardia trophozoites were detected only by the saline mount. The iodine mount was superior to the other mounts for protozoan cyst detection. The concentration procedure enhanced cyst recovery. Faecal preservation and subsequent staining was superior to wet mount examination for detection of the trophozoite stage and avoided the need for fresh specimens. Both the trichrome and the iron haematoxylin stains were comparable for the detection of cysts and trophozoites of the Entomoebae. Giardia lamblia trophozoites stained better with iron haematoxylin than with the trichrome. Preservation and permanent staining is recommended as the most productive means for the accurate identification of the various protozoan parasites.

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