The most critical step in the Gram stain is the application of the:
a. safranin.
b. crystal violet.
c. Gram's iodine.
d. Gram's decolorizer.
Which specimen culture, if positive, should be immediately reported to the clinician?
a. Urine
b. Blood
c. Throat
d. Stool
Bacterial cells with thick peptidoglycan and numerous teichoic acid cross-linkages are Gram stained. The organisms stain pink. Which one of the following statements explains this discre-pancy?
a. The bacterial cells were most likely not heat-fixed to the slide.
b. The bacterial cells were subjected to the decolorizer too long and were overdecolo-rized.
c. The lot of Gram-stain reagent is most likely expired.
d. No discrepancy exists; cells with this composition stain pink on Gram stain.
Transduction is defined as the:
a. change of the bacterial genotypes through the exchange of DNA from one cell to another.
b. internal change in the original nucleotide sequence of a gene or genes within an or-ganism's genome.
c. process by which genetic elements such as plasmids and transposons excise from one genomic location and insert into another.
d. mechanism that is mediated by viruses, by which DNA from two bacteria may come together in one cell, thus allowing for re-combination.
Which specimen is quantitatively plated by using a calibrated loop?
a. Stool
b. Sputum
c. Joint fluid
d. Urine
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