A 19-year-old college athlete presents with a painful, red abscess on his thigh. A wound swab cultured on Mannitol Salt Agar. The plate shows growth with a yellow zone surrounding the colonies. What does this indicate?
The organism cannot tolerate salt
The organism ferments mannitol
The Organism is Gram-negative
The organism produces hemolysin
The Correct Answer is B
A. The organism cannot tolerate salt: Mannitol Salt Agar (MSA) contains 7.5% NaCl, which inhibits the growth of most bacteria except halotolerant organisms. Growth on this medium indicates that the organism can tolerate high salt concentrations, so inability to tolerate salt is not supported by the observation.
B. The organism ferments mannitol: MSA contains mannitol and a pH indicator (phenol red). When bacteria ferment mannitol, acidic byproducts lower the pH, turning the agar yellow around the colonies. The presence of a yellow zone surrounding growth indicates that the organism is a mannitol fermenter, commonly seen with Staphylococcus aureus.
C. The organism is Gram-negative: MSA is selective for Gram-positive bacteria due to its high salt concentration. Gram-negative bacteria are typically inhibited and do not grow well on this medium. Therefore, growth on MSA suggests the organism is Gram-positive, not Gram-negative.
D. The organism produces hemolysin: Hemolysis is detected on blood agar, where lysis of red blood cells produces clear or greenish zones around colonies. The yellow zone on MSA is due to mannitol fermentation and not hemolysin production, so this observation does not indicate hemolysis.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
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.
Correct Answer is A
Explanation
Based on the image provided, the arrow is pointing to the arm of the microscope.
Arm: The arm is the curved or slanted part of the microscope that connects the base to the head (which contains the eyepiece and revolving nosepiece). It serves two main purposes: It holds the upper portion of the microscope (the optical components) securely above the stage. It is the primary part of the microscope designed to be gripped when carrying the instrument.
Shoulder: The shoulder is the upper supporting part of the microscope where the arm meets the head or body tube. It provides structural support for the optical components and helps maintain proper alignment of the microscope parts.
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