Chapter 17 Flashcards
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
What is specificity?
Property of a test to focus on only a certain antibody or antigen; degree to which test does not falsely detect conditon
What is selectivity?
Detection of even minute quantities of antibodies or antigens in a specimen; degree to which test will detect every positive
What is the purpose of polymerase chain reaction (PCR)?
To produce numerous copies of DNA or RNA within hours
What are hybridization probes?
Small fragments of DNA or RNA that are known to be complementary to nucleic acid sequences from particular microbes; base-pairing of the probe indicates microbe presence
What is fluorescent in situ hybridization (FISH)?
Application of fluorescently labeled probes to intact cells within a patient specimen or environmental sample; “glowing cells” indicate microbe presence
What are microarrays?
Absorbent plates or chips that contain gene sequences from thousand of infectious agents; patient samples are incubated on microarrays, and matching sequences hybridize to the chips
What is deep sequencing?
Scanning and analyzing a single genome multiple times to reduce errors
What is genetic fingerprinting?
Method for analyzing short segments of DNA within a sample?
What is pulse-field gel electrophoresis (PFGE)?
Similar to genetic fingerprinting, but involves separation of DNA fragments that are too large for conventional gel electrophoresis
What is PulseNet?
A program established by the CDC that allows for comparison of PFGE data from patient specimens
What are Lab on a Chip tests?
Genetic tests that have been miniaturized and placed on chips that are easy to use, and require few supplies and little technical training
How can imaging be used in infection diagnosis?
Imaging can be used to find areas of localized infection prior to a biopsy, sparing patients an invasive procedure if an infection is not present
What is the Seven Gene Blood Test strategy?
A blood test can be used to check for the presence of seven genes that host cells express in response to bacterial, but NOT viral, infection
What is the Virus Strain Blood Test strategy?
A blood test can scan for antibodies to more than 1,000 strains of 206 virus species
