Ch 15: Diagnosing Infections Flashcards
What are the types of testing that can diagnose infections?
PHENOTYPIC
- Physical or biochemical observations
GENOTYPIC
- Genetic analysis
IMMUNOLOGIC
- Pathogen-specific antibodies produced by host
- Pathogen-specific antigen in host specimen
What are some phenotypic methods for diagnosing infections?
Microscopic examination
- Gram stain
Macroscopic examination
- Culture characteristics
- Selective and differential media
How does a biochemical test (eg. multitest) identify the microbe present?
Add unknown microbe + substrate
If enzyme present in microbe = Product formed (+ result)
If enzyme absent in microbe = No Product (- result)
What are some Genotypic methods for diagnosing infections?
Polymerase Chain Reaction
- exponential amplification
- can be visually detected using gel electrophoresis
Fluorescent in situ hybridization (FISH)
- Fluorescent “tagged” DNA probe is used to detect DNA of the pathogen in a specimen
- “Tag” is visualized by fluorescence microscopy
What are the immunologic methods for diagnosing infections?
Test for antibodies in patient specimen or test for antigens in patient specimen
immunoassay “quick test”
enzyme-linked immunosorbent assay (ELISA)
agglutination reactions
immunofluorescence and microscopy
How do immunoassay quick test work?
“Tagged” antibodies are used to detect antigens of the pathogen
“Tag” is involved in color development
How do enzyme-linked immunosorbent assay (ELISA)
work?
Coat wells with HIV gp120 (antigen)
Add patient blood samples – HIV positive contains antibodies to gp120 (left), HIV negative contains nonspecific antibodies (right)
Wash away unbound antibodies
Add antibody “tagged” with an enzyme that recognizes Fc of bound antibody
Substrate is added that “tag” will convert from clear to yellow
Yellow color indicates presence of anti-HIV antibodies (HIV positive)
How do agglutination reactions work?
antibodies are used to detect pathogen-specific antigens in a patient sample by “clumping” reaction
What is immunofluorescence and microscopy?
Pathogens covered w/ antigens
Antibodies tagged w/ fluorescent molecules
Pathogen “tagged” with fluorescent molecules through antigen-antibody binding
