[BAT] BACTERIAL AGGLUTINATION TEST Flashcards
What is bacterial agglutination?
A serologic test where bacterial antigens react with specific antibodies to form visible clumps.
What is the principle of bacterial agglutination tests?
It is based on the antigen-antibody reaction that results in visible clumping (agglutination).
What are the main bacterial agglutination tests?
Widal test, Weil-Felix test, Brucella agglutination test, and febrile agglutination tests.
What is the Widal test used for?
Diagnosis of typhoid fever by detecting antibodies against Salmonella typhi.
What antigen-antibody reaction occurs in the Widal test?
Agglutination occurs when patient antibodies bind to Salmonella ‘O’ and ‘H’ antigens.
What are the somatic and flagellar antigens in the Widal test?
‘O’ antigen (somatic) and ‘H’ antigen (flagellar) of Salmonella typhi.
What is a positive Widal test result?
A significant titer increase (e.g., 1:160 or higher) in paired serum samples.
What is the Weil-Felix test used for?
Diagnosis of rickettsial infections using Proteus OX antigen cross-reactivity.
Which bacterial strains are used in the Weil-Felix test?
Proteus OX19, OX2, and OXK.
What is the principle of the Weil-Felix test?
Indirect agglutination where Proteus antigens cross-react with rickettsial antibodies.
What diseases can be diagnosed using the Weil-Felix test?
Epidemic typhus, scrub typhus, and Rocky Mountain spotted fever.
What is a positive Weil-Felix test result?
A fourfold rise in titer between acute and convalescent samples.
What is the Brucella agglutination test used for?
Diagnosis of brucellosis, a zoonotic bacterial infection.
What specimen is used for the Brucella test?
Serum.
What type of antigen is used in the Brucella test?
Heat-killed phenolized Brucella antigens.
What is a positive Brucella agglutination test result?
A titer of 1:80 or greater indicates infection.
What are febrile agglutination tests?
Agglutination tests for detecting bacterial infections causing persistent fever.
What bacterial infections are detected using febrile agglutination tests?
Typhoid fever, brucellosis, rickettsial infections, and tularemia.
What are the common bacterial febrile antigens used in testing?
Salmonella, Brucella, Proteus, and Francisella species.
What is the test for diagnosing typhoid fever?
Widal test.
What is the test for diagnosing brucellosis?
Brucella agglutination test.
What is the test for diagnosing rickettsial infections?
Weil-Felix test.
What is the test for diagnosing tularemia?
Agglutination test using Francisella tularensis antigen.
What is the significance of agglutination titer in bacterial agglutination tests?
A rising titer suggests active infection, while a stable titer suggests past exposure.
What is the normal titer for a negative Widal test?
Less than 1:80.
What does a high and rising Widal titer indicate?
Active typhoid fever.
Why is the tube method preferred for confirming bacterial agglutination tests?
It provides a more accurate measurement of antibody levels.
What is the significance of an O antibody titer in Widal testing?
Indicates active infection with Salmonella typhi.
What is the significance of an H antibody titer in Widal testing?
Indicates past infection, vaccination, or convalescence.
What is the difference between active infection and past infection in the Widal test?
High O titer suggests active infection, while a high H titer suggests past exposure.
What are the limitations of the Widal test?
False positives, cross-reactivity, and low sensitivity in vaccinated individuals.
Why is the Weil-Felix test not highly specific for rickettsial infections?
Proteus species also cross-react with other bacterial infections.
How is the Brucella agglutination test performed?
Patient serum is mixed with Brucella antigen, and agglutination is observed.
What is the incubation period for brucellosis before antibodies appear?
1-3 weeks.
What is the role of cross-reactivity in bacterial agglutination tests?
Cross-reactivity can cause false-positive results with other bacteria.
What causes false-positive bacterial agglutination test results?
Prior infections, vaccinations, and non-specific immune reactions.
What causes false-negative bacterial agglutination test results?
Low antibody levels, early infection stage, or immune suppression.
Why should bacterial agglutination tests be interpreted with clinical correlation?
Clinical symptoms and epidemiological history improve test accuracy.
What is the role of serial dilution in bacterial agglutination tests?
It determines the antibody concentration in the sample.
What is the endpoint in a bacterial agglutination test?
The highest dilution at which agglutination is still visible.
What is the significance of prozone phenomenon in bacterial agglutination tests?
Excess antibodies can prevent visible agglutination, causing false-negative results.
How is the Brucella agglutination titer interpreted?
A titer of 1:80 or higher is considered significant.
What are heterophile agglutination reactions in bacterial infections?
Antibodies that cross-react with other bacterial antigens.
What are confirmatory tests for bacterial infections detected via agglutination tests?
Culture, PCR, and enzyme immunoassays.
What are the advantages of slide agglutination tests?
Rapid results, simple procedure, and requires minimal equipment.
What are the disadvantages of slide agglutination tests?
Subjective interpretation and lower accuracy compared to the tube method.
Why is the tube method more reliable than the slide method?
It provides more accurate quantification of antibodies.
What is the importance of antigen standardization in bacterial agglutination tests?
Ensures specificity and sensitivity of the test.
What precautions should be taken while performing bacterial agglutination tests?
Proper specimen collection, avoiding contamination, and following test protocols.
