(R7) MIF solution (merthiolate-iodine-formalin)

This solution enables simultaneous fixing (with formalin) of protozoa and their staining with two coloring agents (iodine and eosin). MIF solution is mainly used for in-the-field investigations.

Advantages:

-       Examination of fresh feces with MIF solution gives prompt diagnosis, showing the presence of any intestinal protozoa (trophozoites or cysts) or helminthic eggs and larvae. The fixed and stained stool specimens can be examined even weeks or months later.

Disadvantages:

-       Protozoa identification is often difficult; the microscopist must be experienced;

-       Permanent stains can be performed on MIF-fixed specimens but the morphology of organisms is not as good as that seen with Schaudinn's, PVA or SAF solutions;

-       The components of MIF solution must be stored separately and mixed only immediately before use;

-       Iodine solution is unstable and must be frequently renewed;

-       Concentration techniques are not always efficient;

-       Merthiolate tincture (containing eosin, 1/1000) it is not readily available commercially.

MIF solution for staining fresh stool specimens

Composition

-     Merthiolate tincture, 1/1000 Lilly®                        7.75 ml

-     Lugol's 5% iodine solution                                   1.00 ml

-     Formalin 37%-40%                                             1.25 ml

This solution is stable for up to 8 hours. The quantity of reagents may be reduced proportionately if needed. For use, see: “Microscopic examination with stains for temporary (wet mount) preparations”.

MIF solution for test tube staining or for fecal specimen storage

MF stock solution

Composition

-     Merthiolate tincture, 1/1000 Lilly®                         200 ml

-     Formalin 37%-40%                                                25 ml

-     Glycerol                                                                 5 ml

-     Distilled water                                                     250 ml

Mix well. Store in a sealed, brown glass bottle. The solution is stable for several months.

Lugol's 5% iodine solution

Composition

-     Iodine crystals                                                          5 g

-     Potassium iodide (KI) crystals                                  10 g

-     Distilled water                                                     100 ml

Procedure

-     Dissolve potassium iodide in 20-30 ml distilled water;

-     Slowly add iodine crystals to get a homogeneous solution;

-     Add the remaining water, mix well and filter.

-     Store in a tightly sealed brown bottle.  The solution is stable for several weeks.  

MIF working solution

Composition

-     MF stock solution                                               2.35 ml

-     Lugol's 5% iodine solution                                   0.15 ml

Immediately before use, add MF stock solution to Lugol's iodine solution, and not vice versa.   For use, see: “Microscopic examination with stains for temporary (wet mount) preparations”.