Short answer: Water samples work best. Soil samples can be tested, but results may be less reliable.
Microbial Source Tracking (MST) is designed to find signs of fecal contamination by detecting specific DNA markers. These markers are most stable and easiest to detect in water, which is the environment MST testing was built for.
In soil, things become more complicated. Microbial DNA can stick tightly to soil particles or break down more quickly, which makes it harder to extract and detect. This can lead to weaker signals or results that are harder to interpret with confidence.
Because of this, water samples almost always provide clearer and more accurate answers.
What to collect instead of soil (recommended)
If there is any water near your area of concern, even a small amount, it is the best option for MST testing.
Good examples include:
- Puddles
- Runoff water
- Drainage areas
- Standing water near the suspected source
These water sources often carry the same microbial indicators as the surrounding soil, but in a form that is easier for the test to detect accurately.
Using a LuminUltra preservation kit with water samples is especially helpful, as it stabilizes the DNA during shipping and helps ensure reliable results.
If soil is your only option
If there is no water available, you can still submit a soil sample. Just keep in mind that results may be less definitive.
You have two options:
Option 1: Standard submission
- Collect about 1 gram of soil from the area of interest
- Place it in a sealed plastic bag
- Ship the sample on dry ice to help preserve the DNA
Option 2: Using a LuminUltra preservation kit
- Use the collection tube included in your kit
- Follow the instructions for solid samples, and add two level scoops of soil into the tube
Why water works better than soil
MST testing is specifically validated for water. In soil:
- DNA can bind to particles, making it harder to extract
- DNA may break down more quickly
- This can lead to weaker or inconclusive results due to matrix interference
Water, on the other hand, keeps the microbial markers more accessible and stable, allowing the test to perform as intended.
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