Tools and Techniques of Microbiology Lab Flashcards
What is the difference between a screening/presumptive test vs a definitive/confirmatory test
Screening/presumptive test= less expensive, rapid, sensitive but less specific test
Definitive/confirmatory test = more expensive, less rapid but more specific test
What is sensitivity
- Can it detect it
- the ability of the test to detect low levels of antigen or antibody when present
What is specificity
- Is it accurate
- the ability of the test to accurately detect only the correct antigen or antibody while not reacting with incorrect antigen or antibody
What are ways to ID microorganisms
- Gram stain
- Culture characteristics via microscopy
- Biochemical test (expression of gene traits)
What are the 4 types of general culture media and there characteristics
- Nutrient= general media that allows bacterial growth
- Enriched= general nutrients plus extras to grow more fastidious bacteria
- Selective= contains ingredients to restrict growth of certain type of bacteria
- Differential= contains ingredients that visually indicate certain chemical reactions by bacterial growth
Describe a Blood Agar Plate
moderately enriched medium that permits visual observation of blood cell hemolysis
What are the 3 categories of hemolysis in a blood agar plate
- Alpha=green around the colony, represents partial hemolysis
- Beta= clear zone around colony, represents complete lysis
- Gamma= no change in RBCs around the colony
Describe a Supplemented Chocolate Agar
highly enriched medium that grows medically significant bacteria, w/o displaying hemolysis
Describe a MacConkey Ager (MAC)
selective and differential (pH) media for gram negative bacilli that
How are yeasts cultured and identified
- Grow on blood agar plates
- ID= microscopy, biochemical test, antigen test
How are molds cultured and identified
-Grow on selective media w/ Abx
-ID= microscopic exam of culture/organism
few antigenic or biochemical test
How are viruses cultured and identified
- Grow in living tissue= not usually done anymore because of cost and time
- ID= antibody detection (did you have it), antigen detection (do you have it now), gene probes
Summarize Immunoassay Reaction Procedures
- Antigens bind to specific antibodies
- Unbound antibodies are washed of, so they will not cross react
- Antibody-Antigen binding is detected
low to moderate sensitivity
What is a Lateral Flow Immunoassay and how does it work
- assay in which a known molecule and detection molecules are embedded in an artificial membrane
- specimen is deposited on one end and is wicked through the membrane to react with the detection molecule
- If the specimen is positive binding becomes visible by deposit of the bound molecules at the test line
What is the Agglutination method
The reaction of particle sized antigen with its corresponding antibody resulting in a macroscopic clumping
low sensitivity
What is immunofluorescence
fluorescent molecule produces light at a detectable wave length when excited by UV light
What is a Enzyme Immunoassay (EIA) or Enzyme Linked Immunosorbent Assay (ELISA) and how does it work
- A known antibody is labeled w/ color producing enzyme
- The labeled antibody is then reacted w/ an unknown antigen and unbound antibodies are washed off
- The antigen-antibody are exposed to a color producing substrate to make the reaction visible
Very sensitive and accurate test
What is a gene probe
test kits that are used to detect the presence of significant gene sequences
What is gene amplification
the process of increasing the number of copies of genes so they can be detected
What 2 gene amplification systems are used in DOD clinical and CBRN labs
BioFire Film Array and Cepheid GeneXpert Omni
When do you use oil immersion
when you need high power 90-100x
What is an antimicrobial susceptibility test
- used to determine if the pathogen is susceptible or resistant to a set of Abx
- decision to use this test is based on clinical significance of the pathogen (ie pathogen is unlikely to have resistance)
Define susceptible in regards to antimicrobial susceptibility test
The microorganism is inhibited by the maximum safe dose of the ABX
Define resistant in regards to antimicrobial susceptibility test
The microorganism is affected by the maximum safe dose of the ABX
Define intermediate in regards to antimicrobial susceptibility test
The microbe maybe inhibited by a high dosage but is near the resistance point and may not be appropriate to use
What is minimum inhibitory concentration (MIC)
test to determine the minimum concentration of each Abx agent that is effective against a pathogen to promote a more precise selection of dosage
True or False an Abx should be 2x the minimum inhibitory concentration (MIC)
True to ensure the concentration is always above MIC
How is minimum inhibitory concentration (MIC) interpreted
susceptible (2x MIC), intermediate, and resistant (2x MIC can not be achieved
What is the disk diffusion testing method
Only used in rapidly growing aerobic and facultative bacteria
Paper disk containing known concentrations of Abx are applied to inoculated agar. A zone of inhibition can then occur, which is then measured and is interpreted using a detailed chart
