Baermannization

In 1917, while working in Java, the Dutch physician Dr. Baermann developed a simple method for isolating nematodes from soil. Today veterinarians use his method for the extraction of live larval stages of nematode parasites from the feces.

1. Place a sieve in a custard dish or other similar container.

2. Spread about 10 grams of fresh feces on a piece of tissue paper and place it into the sieve.

Note: Since you are looking for live larvae, anything which is done to the feces that might kill the larvae should be avoided (i.e. don't let it dry out, don't put it into formalin, don't freeze it, and even keeping it in a refrigerator overnight may impair the larvae's motility).

3. Place warm water* in the custard dish until it just covers the feces, taking care not to disrupt the feces.

4. Allow to sit for about one hour**.

5. Lift off sieve and pour liquid into a 50 ml centrifuge tube.

6. Let sit for 20 minutes.

7. Using a Pasteur pipet, remove a drop of the sediment at the bottom of the tube and place it on a microscope slide for examination. (Be careful not to resuspend the sediment before you take a sample from it.)

Traditional Baermann set-up

Clinical Baermann set-up

Click here for a video demonstration of the Baermann Technique

USES: This technique is used to recover larval nematodes for identification. Larval nematodes are normally not numerous in feces and therefore not seen on a direct smear or sedimentation. They are also damaged by flotation solutions, making identification difficult to detect them. This technique makes use of two characteristics of parasitic larval nematode behavior:

1. *The warmer it is the more active the larva (up to a point: 37 to 40⁰C is as warm as you want to get. You don’t want to cook them!). Also, some nematode larvae are thermotaxic and will move toward the warmer water in the funnel (the surface cools quicker than the middle of the funnel).
2. Most parasitic larval nematodes are poor swimmers.

Therefore, the following events take place when the sieve is placed in the water:
The larvae will be moving around in a random fashion and within any given time interval some of them will migrate through the tissue and fall into the water. Because they can't swim, they sink to the bottom and over time a number accumulate there. The more active (or themotaxic) the larvae are (i.e. the warmer the water) the greater the number of larvae that will accumulate at the bottom in a given time interval.

**The longer you wait the more larvae will fall to the bottom of the dish, but with time the fecal sample also breaks down, leading to an accumulation of sediment along with the larvae.