There are several ways to detect the actions of microbial organisms in the human body, depending on the specific type of microbe bacteria, virus, parasite, e.t.c

Microbial Growth:

Culture Tests: This is a traditional method where a sample from the body (blood, stool, urine, etc.) is placed on a nutrient-rich medium that promotes the growth of specific microbes. If microbes are present, they will multiply and become visible as colonies. This method can identify the type of microbe based on its growth characteristics.

Quantitative PCR (qPCR): This technique uses specific DNA sequences to identify and quantify microbial presence. It’s more sensitive than culture tests and can detect even small amounts of microbial DNA.

Microbial Products:

Antibody Tests: These tests detect antibodies, proteins produced by the immune system in response to a specific microbe. A positive antibody test indicates past or present exposure to a microbe, but not necessarily an active infection.
Antigen Tests: These tests directly detect antigens, molecules on the surface of microbes. A positive antigen test usually indicates an active infection.

Toxin Detection: Some microbes produce toxins that can cause disease. Tests can be done to detect these toxins in body fluids, indicating the presence of a specific toxin-producing microbe.
Microbial Effects:

Microscopy: Direct examination of body fluids or tissues under a microscope can sometimes reveal the presence of microbes. However, this method is not always reliable for identification.

Complete Blood Count (CBC): This blood test can provide clues about a microbial infection, such as an elevated white blood cell count. However, it’s not specific to microbial infections and can be elevated for other reasons.

Imaging Techniques: Depending on the location of the infection, X-rays, CT scans, or MRIs can sometimes show changes caused by the presence of microbes.
Additional factors to consider:

The specific symptoms a person is experiencing will help guide which tests are most appropriate.
No single test is perfect, and often a combination of methods is used for diagnosis.

Interpretation of test results should be done by a healthcare professional in the context of a patient’s medical history and symptoms.