Common Serologic Tests for Bacterial Infection

Questions and Answers

What organism causes syphilis?

Staphylococcus aureus

Treponema pallidum (correct)

Neisseria gonorrhoeae

Escherichia coli

Which microscopy techniques can be used to see Treponema pallidum?

X-ray microscopy

Light microscopy

Electron microscopy

Dark field microscopy (correct)

Which of the following statements about syphilis is true?

Syphilis is primarily transmitted via contaminated water.

Syphilis is the third most common sexually transmitted disease. (correct)

Syphilis cases have been eradicated since the 1940s.

Syphilis can be caused by gram-positive bacteria.

What is the primary mode of transmission for syphilis?

Direct sexual contact Signup and view all the answers

What treatment is Treponema pallidum sensitive to?

Penicillin Signup and view all the answers

Congenital syphilis can occur through which of the following means?

Via placenta from an infected mother Signup and view all the answers

What is the incubation period for primary syphilis?

10–90 days Signup and view all the answers

Which of the following describes a primary chancre in syphilis?

It typically heals within 3-8 weeks without treatment. Signup and view all the answers

What characterizes the secondary stage of syphilis?

Clinical symptoms may include mucosal ulcers and fever. Signup and view all the answers

After the symptoms of secondary syphilis subside, what stage does the disease enter?

Early latent stage Signup and view all the answers

What does the early latent stage of syphilis indicate?

Infection occurred within the past 12 months. Signup and view all the answers

Which symptom is NOT commonly associated with secondary syphilis?

Painless chancre Signup and view all the answers

How does primary syphilis typically present in females?

As a chancre located in the cervix. Signup and view all the answers

What temperature and duration are required to reheat activated serum tested after 4 hours?

56°C for 10 minutes Signup and view all the answers

What is the characteristic of serological tests for syphilis during secondary syphilis?

They are positive in nearly all cases. Signup and view all the answers

Which of the following is NOT a cause of false-positive results in syphilis testing?

Chlamydia Signup and view all the answers

Which fluid can the VDRL test be performed on?

Cerebrospinal fluid Signup and view all the answers

What is one disadvantage of the VDRL test?

The antigen must be prepared fresh daily Signup and view all the answers

How should serum specimens be handled before testing in the VDRL test?

They must be heat inactivated Signup and view all the answers

What does a medium or large flocculation particle result indicate in the VDRL test?

Reactive result Signup and view all the answers

What should be done if sera exhibit slight roughness during VDRL testing?

Quantitate to check for prozone phenomenon Signup and view all the answers

What type of test is the RPR test classified as?

18-mm circle card test Signup and view all the answers

What component is added to the RPR antigen to eliminate the need for heat inactivation of serum?

Choline chloride Signup and view all the answers

What is the main purpose of charcoal particles in the RPR test?

To visualize agglutination Signup and view all the answers

Why might non-treponemal tests like RPR revert to negative after therapy?

Antibody levels decrease after successful treatment. Signup and view all the answers

What aspect of non-treponemal tests is considered a limitation?

Results can be interpreted subjectively. Signup and view all the answers

Which condition is NOT likely to cause a false positive in non-treponemal tests?

Thyroid disease Signup and view all the answers

What does a uniform gray result in the RPR test indicate?

Lack of agglutination Signup and view all the answers

Which of the following is a characteristic of non-treponemal tests like RPR?

Provide results in minutes. Signup and view all the answers

What is a common feature of non-treponemal assays like RPR and VDRL?

They involve agglutination assays. Signup and view all the answers

What type of antibodies are produced first during a rickettsial infection?

IgM antibodies Signup and view all the answers

What is the principle behind the Weil-Felix test?

Antigenic cross-reaction between serotypes Signup and view all the answers

Which Proteus species antigen reacts with antibodies to the scrub typhus group?

OX-K Signup and view all the answers

In the Weil-Felix test, which organism is associated with a strong reaction to OX-19 antigen?

R. prowazekii Signup and view all the answers

Which of the following OX antigens is NOT associated with the typhus group antibodies?

OX-K Signup and view all the answers

What cross-reaction activity is considered for the establishment of the Weil-Felix test?

Between Proteus spp and Rickettsia spp Signup and view all the answers

Which Proteus species antigens can react with antibodies to the spotted fever group?

OX-2 and OX-19 Signup and view all the answers

How is the Weil-Felix test interpreted in terms of reactions?

Positive reactions correspond to specific Rickettsial groups Signup and view all the answers

Study Notes

Syphilis Overview

Caused by the spirochete Treponema pallidum, a Gram-negative motile organism.
Unable to grow in artificial media; undetectable by light microscopy due to size (0.15 μm in diameter, 5-15 μm in length).
Visible through dark field microscopy and phase contrast techniques.
Stainable using silver impregnation and fluorescent antibody techniques.
Sensitive to penicillin.

Epidemiology

Incidence declined significantly post-1940s due to penicillin.
Over 70,000 new cases reported annually.
Third most common sexually transmitted disease (STD), chronic and slowly progressive.

Mode of Transmission

Primarily through direct sexual contact (90-96% of cases).
Can also spread via blood transfusion or from an infected mother to fetus during pregnancy (congenital syphilis).
Accidental exposure is possible, particularly for medical personnel.

Clinical Features

Incubation Period: 10 to 90 days (average 21 days).
Symptoms vary across stages of infection.

Primary Syphilis

Characterized by a single, painless chancre appearing 2-10 weeks post-exposure.
Chancre is usually indurated and located on the genitalia (90%) or lips (5-10%).
In females, the chancre may occur in the cervix.
Fluid from the chancre is highly infectious; spirochetes can be identified using dark field microscopy.
Chancre typically heals spontaneously in 3-8 weeks; positive serological tests in 80% of cases.

Secondary Syphilis

Occurs 6-8 weeks after the primary chancre resolves.
Features disseminated lesions including skin rashes, mucosal ulcers, and condylomata.
Other symptoms include lymphadenopathy, fever, headache, and malaise.
Highly infectious stage with near-universal positivity in serological tests.
Can progress to early latent, late latent, or tertiary syphilis stages.

Latent Stage

Defined by positive serology in the absence of clinical symptoms.
Early latent refers to infections acquired within the last 12 months.

Serological Testing

Tests must account for heat inactivation if performed more than 4 hours after original sample collection; cerebrospinal fluid is also valid for testing.
False-Negative Results: Possible in the first three months of syphilis infection or during late stages.
False-Positive Results: Can occur due to various conditions like HIV, Lyme disease, malaria, systemic lupus erythematosus, etc.

Non-Treponemal Tests

VDRL Test:
- Performed on serum or CSF; must use fresh antigen.
- Requires heat inactivation and microscopic reading for results.
- Reactive tests have medium/large flocculation; non-reactive tests show dispersion or slight roughness.
RPR Test:
- Macroscopic circle card test featuring cardiolipin, cholesterol, and lecithin antigen mixed with unheated serum.
- Presence of antibodies leads to agglutination, visible as black clumps against a white background.
- Quick results, inexpensive, and does not require specialized equipment.
- Can help monitor treatment response.

Limitations of Non-Treponemal Tests

Subjective results and nonspecificity may lead to false positives from various conditions like lupus and Epstein-Barr virus.

Weil-Felix Reaction

An agglutination test based on cross-reactivity of antigens between some Proteus and Rickettsia species.
Uses Proteus antigens OXK, OX2, and OX19 to detect antibodies associated with rickettsial infections.
Cross-reactions help diagnose different rickettsial groups:
- Typhus group reacts with OX19.
- Scrub typhus group reacts with OXK.
- Spotted fever group reacts with both OX2 and OX19.

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Description

Explore the serological tests commonly used for bacterial infections, focusing on syphilis serology. Learn about the causative agent Treponema pallidum and the characteristics of this spirochete organism. This quiz will help you understand the essential aspects of diagnosing syphilis and its implications.

Common Serologic Tests for Bacterial Infection - Chapter 3