A 7-year-old child presents with fever, sore throat, and swollen anterior cervical lymph nodes.
A throat swab is cultured on blood agar. After 24 hours, colonies show a clear zone surrounding each colony. Which hemolysis pattern is observed?
Alpha hemolysis
Beta hemolysis
Gamma hemolysis
Delta hemolysis
The Correct Answer is B
A. Alpha hemolysis: Alpha hemolysis produces a partial or greenish discoloration of the blood agar around bacterial colonies due to the reduction of hemoglobin to methemoglobin. It is typically observed with organisms like Streptococcus pneumoniae and viridans streptococci, not clear zones.
B. Beta hemolysis: Beta hemolysis is characterized by complete lysis of red blood cells, resulting in a clear, transparent zone surrounding each colony on blood agar. This pattern is seen with pathogens such as Streptococcus pyogenes (group A strep), which commonly causes fever, sore throat, and anterior cervical lymphadenopathy in children.
C. Gamma hemolysis: Gamma hemolysis indicates no hemolysis; the agar surrounding the colonies remains unchanged. Organisms that exhibit gamma hemolysis, such as some Enterococcus species, do not lyse red blood cells and are typically non-pathogenic.
D. Delta hemolysis: Delta hemolysis is not a standard classification used in clinical microbiology for blood agar patterns. Hemolysis is typically described as alpha, beta, or gamma, with delta being an outdated or rare term not commonly applied to clinical isolates.
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 C
Explanation
A. Lactose: Lactose in Eosin Methylene Blue (EMB) agar serves as a fermentable carbohydrate source. It allows differentiation of bacteria based on their ability to ferment lactose, producing color changes in the colonies, but it does not inhibit Gram-positive bacteria.
B. Agar: Agar is a solidifying agent that provides a stable surface for microbial growth. It is inert and does not selectively inhibit any bacterial group; its role is purely structural.
C. Eosin and methylene blue dyes: The eosin and methylene blue dyes in EMB agar act as selective agents that inhibit the growth of Gram-positive bacteria while allowing Gram-negative bacteria to grow. These dyes also serve as pH indicators, producing color changes in colonies that ferment lactose, which aids in differentiation of coliforms and other Gram-negative bacteria.
D. Sodium chloride: Sodium chloride maintains osmotic balance in the medium but does not selectively inhibit Gram-positive bacteria. Its concentration is not sufficient to act as a selective agent in EMB agar.
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