After Gram staining, Gram-positive bacteria appear:
Pink
Red
Purple
Colorless
The Correct Answer is C
A. Pink: Pink indicates Gram-negative bacteria, which do not retain the crystal violet stain during the decolorization step and are counterstained with safranin. Gram-positive bacteria are not pink after Gram staining.
B. Red: Red is another way to describe the color of Gram-negative bacteria after counterstaining with safranin. Gram-positive bacteria do not take up the red counterstain because they retain the primary crystal violet stain.
C. Purple: Gram-positive bacteria appear purple after Gram staining. Their thick peptidoglycan cell walls trap the crystal violet-iodine complex even after alcohol or acetone decolorization, allowing them to retain the purple color and be distinguished from Gram-negative bacteria.
D. Colorless: Colorless cells would indicate a failure to stain or a decayed sample. Gram-positive bacteria are never colorless after a proper Gram staining procedure.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Alpha hemolysis is characterized by partial lysis of red blood cells on blood agar, leading to a greenish or brownish discoloration around bacterial colonies rather than a clear zone. This occurs because the bacteria produce hemolysins that oxidize hemoglobin to methemoglobin, causing the greenish hue, but do not completely lyse the red blood cells. In contrast, beta hemolysis results in complete destruction of red blood cells and a clear zone surrounding the colonies. Therefore, alpha hemolysis produces incomplete hemolysis with color change rather than full destruction and clearing of the agar.
Correct Answer is A
Explanation
Coarse adjustment: The arrow points to the coarse adjustment knob, a large focusing knob on the microscope used to move the stage up or down quickly to bring the specimen into general focus. It is typically used with low-power objective lenses to locate the specimen and obtain an initial image. Using it with high-power lenses can risk damaging the slide or lens because it moves the stage in large increments.
Fine adjustment: A smaller focusing knob that moves the stage very slightly to sharpen the image after the specimen has been brought into general focus. It is mainly used with high-power or oil immersion objectives to achieve precise, clear visualization of cellular details without risking damage to the specimen.
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