FAUST TECHNIQUE: FOUNDATION AND MATERIALS, STEPS, ADVANTAGES, DISADVANTAGES - MEDICINE - 2025

The Faust technique is a methodology that allows the concentration of some eggs and / or larvae of parasites contained in the feces by floating. It is used when direct coproparasitological tests are negative or when you want to obtain clean samples free of detritus.

Concentration methods for coproparasitological examinations are of three types: by flotation, by sedimentation or by methods that combine the previous two. These methods increase the chances of positive results.

Stool analysis.

The Faust method consists of mixing part of the stool sample with a substance denser than the eggs or parasites to be concentrated. This causes that, being less dense, they float on the surface. The supernatant fluid is collected and viewed under a microscope for identification and quantification.

This method is used to visualize helminth eggs. At the same time, it has proven to be a very sensitive method for the diagnosis of Giardia lamblia, a flagellated protozoan that is widespread worldwide. Flotation methods are not recommended for very heavy parasite eggs such as tapeworms and trematodes.

Parasites are one of the most widespread intestinal infections worldwide, especially in poor countries with poor sanitary measures. For this reason, having sensitive methods to identify and quantify these parasites is very useful for diagnosis and treatment.

Foundation and materials

The technique is based on the existence of different specific gravities of eggs, parasites, cysts, larvae and detritus, using zinc sulfate solutions as a flotation method.

The rationale for the technique is to mix the sample with a zinc sulfate solution that has a density greater than that of lighter eggs, larvae, or parasites.

This allows the heavier elements to precipitate and the lighter ones to float that appear in the supernatant after centrifugation of the samples.

materials

Containers for collection of fecal samples (Source: Bobjgalindo via Wikimedia Commons)

- Prepare a zinc sulfate solution with a density of 1.18 or 1.2 g / ml if the sample was previously treated.

- Prepare a rack with previously labeled test tubes.

- Have a centrifugal machine.

- Have microscope slides and coverslips on hand. All must be labeled

- Make sure that a Lugol's solution is available to stain the sheets.

- Have gauze to filter.

- Have funnels and distilled water.

- Locate labeled plastic or cardboard containers.

- Also applicators and sterile handle of 5 mm.

- A lighter to sterilize the handle.

Steps

Macroscopic and microscopic examination

For any stool examination, the examination begins with what is called the "gross examination" of the samples.

The consistency, color, presence of what appears to be blood, the presence of mucus, and the presence of adult parasites are described.

Then we proceed to the "microscopic examination" of the stool, this depends on the method. The simplest is the direct smear method, which is the simplest microscopic observation method for parasites.

Photograph of the observation of Gardia lamblia, an intestinal parasite (Source: Riddlemaster via Wikimedia Commons)

The procedure involves placing a small amount of the sample directly on a slide. Place several drops of saline solution that should be similar in size to the sample. Mix the saline solution with the stool until a homogeneous mixture is formed. Place a coverslip and examine under the microscope.

Original Faust technique

The second procedure consists of the Faust float method, whose original version consists of:

1- Place about two grams of feces in a suitable container for this purpose.

2- Add 30 ml of zinc sulfate flotation solution with which an emulsion is made by mixing the solution with the feces.

3- Strain with a metal strainer into a second container and transfer to a test tube.

4- Add more flotation solution until a meniscus forms in the tube.

5- Place a glass coverslip on the meniscus. Let it rest for 10 to 15 minutes.

6- Remove the coverslip and place it on a slide, which will be examined under a microscope.

Faust technique by centrifugation

Originally the method did not use centrifugation, however, it is now included as better results are obtained. The technique involves a series of steps to achieve a proper procedure, these are as follows:

1- The feces are washed with water, mixed well and then filtered with gauze folded in four. The sample is placed in a test tube.

2- Centrifuge and remove the supernatant (samples that are kept above water). Steps 1 and 2 are repeated until the supernatant is "clear".

3- Zinc sulfate is added to the filtered and centrifuged sample.

4- It mixes well.

5- Centrifuge again for 1 minute at 2500 rpm (revolutions per minute).

6- The supernatant is recovered with a sterile loop of about 5mm; the tubes should not be shaken.

7- The sample recovered from the supernatant is placed on a slide and a drop of Lugol can be placed to color, the coverslip is placed and observed under a microscope.

8- The containers and test tubes are labeled.

Advantage

- The elements used for the diagnosis can be seen clean and without “detritus”, this facilitates the observation of the sheet and reduces the time used for the diagnosis.

- In the supernatant, both larvae, eggs and / or cysts are recovered.

- It is a very low cost method.

- The procedure is very simple and easy to implement.

- The diagnosis is fast and accurate.

- Due to the importance and high incidence of parasitosis in poor countries, these low-cost and easy-to-use methods are ideal for the diagnosis and monitoring of these pathologies.

Disadvantages

The density of the flotation solution produces a contraction of the larvae, that is, they shrink and, in a very short period, can deform. This forces the examiner to make the diagnosis immediately and the treated samples cannot be kept for future examinations.

As with all microscopic identification methods, a highly experienced examining staff is required to make accurate diagnoses.

The rapid deformation of the elements necessary for the diagnosis, although they are an obvious disadvantage, can be corrected by making immediate microscopic observations.

References

1. Ananias, FL (2017). Evaluation of the sensitivity of Faust method and spontaneous sedimentation for the diagnosis of giardiasis. Cuban Journal of Tropical Medicine, 68 (2).
2. Bartlett, MS, Harper, K., Smith, N., Verbanac, P., & Smith, JW (1978). Comparative evaluation of a modified zinc sulfate flotation technique. Journal of clinical microbiology, 7 (6), 524-528.
3. Becker, AC, Kraemer, A., Epe, C., & Strube, C. (2016). Sensitivity and efficiency of selected coproscopical methods-sedimentation, combined zinc sulfate sedimentation-flotation, and McMaster method. Parasitology research, 115 (7), 2581-2587.
4. Garcia, LS, Arrowood, M., Kokoskin, E., Paltridge, GP, Pillai, DR, Procop, GW,… & Visvesvara, G. (2018). Laboratory diagnosis of parasites from the gastrointestinal tract. Clinical microbiology reviews, 31 (1), e00025-17.
5. Summers, WA (1942). A modification of zinc sulfate centrifugal flotation method for recovery of helminth ova in formalinized feces. Journal of Parasitology, 28 (4), 345-346.