Читать книгу Practical Guide to Diagnostic Parasitology - Lynne Shore Garcia - Страница 82

Both the concentration and the permanent stained smear can be performed from specimens preserved in SAF, and the formula has the advantage of not containing mercuric chloride, as is found in Schaudinn’s fluid and mercuric chloride-based PVA fixatives. It is a liquid fixative, much like the 10% formalin described above. The sediment is used to prepare the permanent smear, and it is frequently recommended that the stool material be placed on an albumin-coated slide to improve adherence to the glass.

SAF is considered to be a “softer” fixative than Schaudinn’s or mercuric chloride-based PVA fixatives. The organism morphology is not quite as sharp after staining as are organisms originally fixed in solutions containing mercuric chloride. The pairing of SAF-fixed material with iron hematoxylin staining provides better organism morphology than does staining of SAF-fixed material with trichrome (personal observation). Although SAF has a long shelf life and is easy to prepare, the smear preparation technique may be a bit more difficult for less experienced personnel who are not familiar with fecal specimen techniques. Laboratories that have considered using only a single preservative have selected this option. Helminth eggs and larvae, protozoan trophozoites and cysts, and coccidian oocysts and microsporidian spores are preserved using this method.

SAF fixative is prepared as follows:

Sodium acetate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 g

Acetic acid, glacial. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 ml

Formaldehyde, 37–40% solution. . . . . . . . . . . . . . . . . . . . . . . 4.0 ml

Distilled water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.0 ml

To make Mayer’s albumin, mix equal parts of egg white and glycerin. Place 1 drop on a microscope slide, and add 1 drop of SAF-preserved fecal sediment (from the concentration procedure). After mixing, allow the smear to dry at room temperature for 30 min prior to staining.

Summary: SAF