Environmental Monitoring & Assessment Flashcards
7 cards from real PCR practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Environmental Monitoring & Assessment flashcards as text
A lab performs routine wipe tests of benches in the post-amplification room. Which result most strongly indicates amplicon carryover contamination?
Answer: Target amplified from bench swabs at Ct values around 25
Early-Ct target signal from surface swabs shows a heavy load of amplified product on the work surface.
Which sampling approach is best for recovering DNA contamination from a pipette barrel surface?
Answer: Swab moistened with sterile, nuclease-free water or buffer
A moistened swab picks up dried nucleic acid from surfaces much better than a dry swab.
Several consecutive runs show positive no-template controls (NTCs) with similar Ct values across all wells. What is the most likely source?
Answer: Contaminated shared reagent such as master mix or water
The same contamination level in every NTC points to a shared reagent, not to random aerosol events.
Why should environmental swab monitoring include a negative swab control (an unused swab processed alongside samples)?
Answer: To confirm the swabs and extraction reagents are not themselves contaminated
An unused swab control shows whether contamination comes from the sampling materials rather than the surface.
Freshly prepared 10% household bleach is preferred for PCR surface decontamination mainly because it:
Answer: Oxidizes and fragments nucleic acids so they cannot be amplified
Sodium hypochlorite oxidatively damages DNA, leaving it unamplifiable.
After bleaching a bench, why is it recommended to wipe the surface with 70% ethanol or water?
Answer: To remove bleach residue that can corrode surfaces and inhibit later reactions
Leftover hypochlorite corrodes equipment and can carry over into reactions and inhibit them.
An environmental monitoring program finds contamination only on the door handles of the pre-PCR room. What corrective action best addresses the root cause?
Answer: Reinforce glove changes and the one-way workflow so staff do not enter pre-PCR from post-PCR areas
Contaminated handles suggest people are carrying amplicons from post-PCR areas, which is fixed through workflow and glove discipline.
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