Serology Strep A and Syph practical

What is the causative agent of syphilis?

Treponema pallidum, a motile spirochete that cannot be cultured in vitro.

How is syphilis transmitted?

Primarily through sexual contact, but also congenitally, through blood transfusion, or by direct contact with infectious lesions.

What is the hallmark lesion of primary syphilis?

A painless chancre at the site of infection.

Which stage of syphilis presents with a rash on the palms and soles?

Secondary syphilis.

What are the two main categories of serologic tests for syphilis?

Nontreponemal (RPR, VDRL) and Treponemal (FTA-ABS, TP-PA).

What antigen complex is used in RPR and VDRL tests?

Cardiolipin-lecithin-cholesterol complex.

What is added to the RPR antigen suspension to visualize the reaction?

Charcoal particles that produce black clumps in a positive result.

Which nontreponemal test is used for CSF testing?

VDRL.

What causes biological false positives in RPR testing?

Conditions like pregnancy, autoimmune diseases (SLE), and infections such as hepatitis or HIV.

How do RPR titers change throughout the stages of syphilis?

Low in primary, high in secondary, decrease in latent/tertiary, and decline after treatment.

What are common technical errors that can affect RPR results?

Improper timing, incorrect rotation, prozone effect, and dirty slides.

What is detected by nontreponemal tests such as RPR and VDRL?

Reagin antibodies that react with cardiolipin antigen.

What organism causes Group A strep infections?

Streptococcus pyogenes (Group A beta-hemolytic strep).

What is the most common Group A strep infection?

Acute pharyngitis (strep throat).

Name two major nonsuppurative sequelae of Group A strep infection.

Rheumatic fever and post-streptococcal glomerulonephritis.

What is the function of the M protein in Streptococcus pyogenes?

It prevents phagocytosis and mimics human tissue antigens, contributing to autoimmune cross-reactions.

What is molecular mimicry and how does it relate to rheumatic fever?

Antibodies against M protein cross-react with cardiac tissue, causing autoimmune inflammation of the heart.

What is the immune mechanism that causes post-streptococcal glomerulonephritis?

Immune complex deposition in the glomeruli leading to complement activation and inflammation.

What does the Anti-Streptolysin O (ASO) test detect?

Antibodies to streptolysin O, indicating a recent Group A strep infection.

What is one advantage and one disadvantage of rapid Strep A antigen testing?

Advantage: Quick results in 10–15 minutes.
Disadvantage: Lower sensitivity; negative results may require culture confirmation.

Why is molecular testing (PCR) useful for diagnosing Strep A infections?

It provides high sensitivity and specificity, detecting small amounts of bacterial DNA.

What does the TP-PA Treponemal test detect, and how is a positive result shown?

Detects antibodies to Treponema pallidum; positive shows diffuse pink agglutination, negative shows a compact red button.

How can immune activation in Strep A infections cause false positives in RPR?

Cross-reactive antibodies may nonspecifically bind to cardiolipin antigen