The disease syphilis is caused by the Treponema pallidum bacteria. The image above is showing which method of determining if a patient has been infected with Treponema pallidum bacteria?

• A. Indirect FA test.
• B. Direct FA test.
• C. Subjective FA test.
• D. Secondary antibody test.

Answer: (A)

Verified step by step guidance

1. Step 1: Identify the components in the image. The green spiral shapes represent the Treponema pallidum bacteria, and the purple Y-shaped structures are antibodies.
2. Step 2: Notice that the antibodies are binding to the bacteria, and there are additional antibodies attached to the first set of antibodies. The secondary antibodies are labeled with a fluorescent marker (indicated by the glowing green circles).
3. Step 3: Understand the difference between direct and indirect fluorescent antibody (FA) tests. In a direct FA test, fluorescently labeled antibodies bind directly to the antigen (bacteria). In an indirect FA test, unlabeled primary antibodies bind to the antigen, and fluorescently labeled secondary antibodies bind to the primary antibodies.
4. Step 4: Since the image shows secondary antibodies binding to primary antibodies that are attached to the bacteria, this indicates the use of an indirect FA test.
5. Step 5: Conclude that the method shown in the image is the indirect fluorescent antibody (FA) test used to detect if a patient has been infected with Treponema pallidum bacteria.