Chapter 17 Flashcards
(38 cards)
What are the three categories of tests used to identify a pathogen?
Phenotypic, immunologic, genotypic
What are the two steps to identifying a pathogen?
- Analyzing patient for signs of microbial infection
2. Specimens are collected and analyzed
What two types of media are used to cultivate specimens for identification?
Selective media and differential media
What microbe characteristics can be observed once a pure culture is obtained?
Microscopic morphology/staining, cultural appearance, motility, oxygen requirements, biochemical analysis, antimicrobial sensitivity tests
What is the basis for biochemical tests?
Enzyme-mediated metabolic reactions
What are the predominant biochemical tests?
- Carbohydrate fermentation
- Hydrolysis of various polymers
- Actions of enzymes
- Identification of metabolism by-products
What is antimicrobial susceptibility testing?
Method used to determine which drugs can be used in treatment
Why is it important to focus on the number of microbes present when determining clinical significance?
A small colony of normal biota is not of concern, but large colonies or normal biota or any colonies of true pathogens are of concern
What is serology?
In vitro diagnostic testing of serum based on the concept that antibodies have extreme specificity for pathogens
What are the two methods of diagnostics within serology?
- An unknown antibody can be detected using a known antigen
2. An unknown antigen can be detected using a known antibody
How are antibody-antigen interactions determined?
Clumps or aggregates of cells/complexes can be seen with the naked eye or by using a microscope
What are the essential differences between agglutination and precipitation?
Size, solubility, and location of antigen
What is the antigen of agglutination?
Antigens are whole cells or cells displaying surface antigens
What is the antigen of precipitation?
Antigens are soluble molecules
How do agglutination and precipitation work?
The antigen is interlinked by several antibodies to form insoluble aggregates that settle out of solution
What are immunochromatography tests?
Tests consisting of a plastic cartridge that directs fluid flow in one direction where it will encounter antibodies; antibody-antigen reactions result in color changes
What is titer?
The concentration of antibodies in a sample, defined by the highest dilution of serum that still produces agglutination
What are fluorescent antibodies (FAb)?
Antibodies labeled by a fluorescent dye
What is direct immunofluorescence testing?
Tests for the presence of an antigen using an FAb
What is indirect immunofluorescence testing?
Tests for the presence of an antibody to an antigen using FAb antibodies that recognize the antibodies in patient sera
What is Enzyme-Linked Immunosorbent Assay (ELISA) testing?
Use of an enzyme-linked indicator antibody to visualize antigen-antibody reactions
What is a direct ELISA test?
Known antibody is adsorbed to a well and incubated with unknown antigen; if antigen-antibody complex forms, secondary antibody will be attracted and a color change will occur
What is an indirect ELISA test?
Known antigen is mixed with patient’s serum; if antigen-antibody complex forms, it will remain in the well after being rinsed; secondary antibody with an added enzyme can then bind to the patient’s antibody, and dye-releasing substrate for the enzyme will be added to produce color change
What is in vivo testing?
Antigen or antibody is introduced into a patient to elicit some sort of visible reaction
