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5. Bacterial serology


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What's the other name for Group strep A?
Strep pyogenes
What are the cellular antgens on Strep A?
-M protein

-Group-specific polysaccharide
What extracellular products does Strep A produce?
-Streptolysin O
-DNAse A/B/C/D
-Erythrogenic toxin
What are suppurative strep infections?
ones producing pus;

ones not producing pus
What are the suppurative strep infections?
-pharyngitis/tonsilitis/strep throat
-scarlet fever
-sinusitis/otitis media
-necrotizing fasciitis
what are the nonsuppurative strep infections?
-Rheumatic fever
-Acute glomerulonephritis
why are some infections better tested serologically?
if the infectious organism is not obtainable on a specimen.
which infections may be better tested with serologic methods?
cellulitis/skin infections
sinusitis/otitis media
finish this one
what are 4 serological tests for strep A?
1. Antistreptolysin O (ASO)
2. ASO Latex agglutntion-rapid
3. Anti-DNAse B (ADN-B)
4. Anti-Hyaluronidase (AHT)
What type of specimen is best for any of them?
Paired sera, 3 weeks apart
what if no paired sera is available?
Compare the convalescent specimen to a reference range.
How does the ASO classic test work?
1. Serum + Streptolysin O added, incubate 15 min at 37'C.
2. Add 5% RBC suspension, incubate 30 min at 37'C.
3. Centrifuge, look for hemolysis
In the classic ASO, what is:
Pos = no hemolysis
Neg = hemolysis; no ASO was present to neutralize the antigen added, so it bound to RBCs and caused lysis.
What type of RBCs are used in the ASO test?
-Human group Oneg
-Rabbit RBCs
How is the titer reported in the ASO test?
The reciprocal of the highest dilution showing NO HEMOLYSIS.
What is the ref range for ASO?
<166 Todd units
What controls are run with the ASO?
1. RBC control - only cells, to make sure not auto-hemolysis.
2. ASO control - Buffer, reagent, and RBCs to make sure hemolysis CAN occur.
3. Standard - to see what 166 Todd units looks like.
What are 3 sources of error in the classic ASO test?
1. Oxidation of reagent from shaking/aerating vial
2. Reconstituted reagent older than 10 minutes.
3. Lipoprotein, cholesterol, bacterial contamination.
How does the rapid ASO test work?
1. Latex beads coated with antigen (streptolysin O).
2. Add serum; look for agglutination.
What should occur if the rapid ASO is positive?
The lab tech should do a quantitative test.
What is the ref range for the rapid aso test?
<200 U/ml
What are 4 sources of error in the rapid ASO?
1. Bacterial contamination
2. Reaction read beyond 3 min
3. Lipemic serum - nonspecific
4. Subjective readings
Along with the classic/rapid ASO tests, what is used for Strep A?
ADN-B test
What type of test is the ADN-B test?
Neutralization test
What is the ADN-B principle?
-Serum and Strep DNAse B are incubated 20 min at body temp.
-Inc w/ DNA-methyl grn overnite
Clear = neg; DNAse worked
Green = pos; the strep's DNAse beat the added to substrate.
How do you report the titer of the ADN-B test?
Reciprocal of highest dilution showing 3+ green.
What is the ADN-B ref range for
Preschool: <120
Other: <1360
What mainly causes error in the ADN-B test?
dnase from organisms other than StrepA
What is one other test that can be used but is uncommon?
AHT - anti-hyaluronidase test
What is the advantage of the ASO test?
-ASO titer rises within 7 days of disease onset.
What are disadvantages of the ASO test?
-Many people have low titers already, b/c of freq. exposure.
-Strep skin infections may produce low titers, undetected
-False + from rising titer in rheumatic fever.
-Only half of glomeruloneph. patients show high titer.
What is the advantage of the ADN-B test?
What is its limitation?
-Most reliable test for Strep A

Titer rises later than ASO.
What disease is Mycoplasma pneumoniae responsible for?
walking pneumonia
How is M. pneumoniae tested for?
-Culture but it takes up to a month to grow!
What 3 serological methods are used for mycoplasma?
1. Complement fixation
2. EIA
3. Cold agglutinins
What is the principle of the cold agglutinins test?
M. pneumoniae agglutinates human group O RBCs in the cold.
What are limitations of the cold agglutinins test?
-The agglutinins are only in 50% of cases.
-Other viral resp diseases can also stimulate cold agglutinins.
what diseases are assoc. with Helicobacter pylori?
-Peptic ulcers
What 4 specimen types are tested for H. pylori? How?
1. Mucosa - Endoscopic biopsy
2. Serum - Serology
3. Stool - EIA for Ag in
4. Breath - Urea tests
What is the CLO test?
a urease test done on endoscopic biopsies for h. pylori.
What do serological H. pylori tests look for?
Antibody in serum to the bug.
What are adantages and disadvntg of serological methods for h. pylori?
Advntg: less invasive than endoscopic biopsy
Disadvntg: less specific and sensitive.
which test for h pylori is best? why?
Urea breath tests - have the highest combined sens./specificty.
What is febrile agglutinins testing used for?
Identifying hard-to-grow microorganisms that often cause fever of unknown origin.
What 4 bacterial diseases are included in a febrile agglutinin panel?
1. Salmonella somatic/flagellar antigens (typhi/paratyphi)
2. Brucella abortus
3. Francisella tularensis
4. Rickettsia
What is the Weil-felix test?
A presumptive test for Rickettsial antibodies
What is the principle of the Weil-felix test?
Rickettsia antibodies cause positive reaction
what is the major limitation of the weil-felix test?
-Antibody detected is heterophilic and nonspecific.
-If Proteus is causing the infection, will get a false pos.
what is the lab's role in diagnosing lymes disease?
-Culture impractical - time
-Serology is most used method.
What are the problems with serological methods for lymes?
-Tests/reagents not standardizd.
-Tests have low sensitivity
Which seroloical methods are used for screening lymes?
What specimens?
IFA - lo volume
Elisa - hi volume
What confirms lymes diagnosis?
-Four fold paired sera titer
-Western blot
what type of fluid can PCR be used on for lymes? What is the problem with this test type?
-Synovial fluid
-Can detect both viable and nonviable lymes.

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