WEEK 11: 11.3 Diagnostic and Laboratory Testing Flashcards
(12 cards)
Describe the diagnostic schema of detection & identification of bacteria
- symptomatic patient - shows signs and symptoms
- make a presumptive clinical diagnosis based on symptoms
- review treatment options and if successful, result in asymptomatic patient
- if a diagnosis isn’t obvious, then must undergo the process of specimen collection (sputum, tissue, biopsy, serum, urine)
- select tests (PCR, serologic, culture, biochemical, gram stain, mass spec)
- definitive diagnosis (antimicrobial susceptibility testing) hence be able to make a successful treatment option
Describe a genetic test that can be used to detect and identify bacteria
Real Time PCR:
amplified targets are fluorescently tagged
cycle threshold/quantification cycle is measures, and cycle in which sample exceeds threshold fluorescence indicates how much DNA is present.
lower Ct= more DNA present
Describe serologic tests and how they detect and identification of bacteria?
They rely on monoclonal antibodies
the binding at test line (specific interaction between mAb and antigen results in a colour change, and this confirms rapid immunoassay validity.
What is a drawback and benefit to serologic tests
they are indicative rather than definitive
the test results are obtained rapidly
why are multiple tests combined to achieve a definitive diagnosis? provide an example
To account for drawbacks in specificity and sensitivity.
glutamate dehydrogenase (high sensitivity, low specificity as it cannot distinguish toxigenic strains) is combined with toxin A/toxin B to test for clostridioides difficile (low sensitivity as it creates false negatives, high specificity)
can also be combined with NAATs which have high specificity and sens but are more time consuming
What are the differential media that increase effectiveness of agar plates in detecting and identifying bacteria
Enrichment - allows growth of many types of bacteria
Selective characteristics - allows growth of selected groups of bacteria
Differential characteristics - allows growth of a number of types of bacteria
Give an example of a selective and differential property of mannitol salt agar
selective: salt inhibits growth of non-halotolerant bacteria
differential: mannitol sugar - fermented by S aureus but not staphylococcus epidermidis
What is a biochemical test that can be used to detect and identify bacteria . describe it
Catalase assay
H2O2 is a by product of metabolism of bacteria
The breakdown can damage DNA
Hence catalase is used to circumvent this damage
catalase can be used to differentiate streptococcus (catalase -ve) and staphylococcus (catalase +ve)
What are three microscopy techniques used to detect and identify bacteria?
Gram stain:
gram + and gram - show in different colours after being stained
Acid fast stain
Spore stain (not as rapid or definitive)
What is an analytic technique used to detect and identify bacteria, briefly describe it and its benefits/drawbacks
Mass spec
peaks relate to specific molecules and can be compared to bacteria composition
adv- rapid and high sens/specificity
disadv- requires access to database of sample spectra, may need sample culture prior to testing
What key areas does lab stewardship focus on?
- appropriate test selection
- secure + accessible data management
- correct interpretation of test results
- sustainable financial resourcing
What are the goals of lab stewardship
- appropriately utilize clinical lab services
- improve quality of patient care
- reduce cost to patients, hospitals and health systems
