The goal of streaking is to Not evenly spread bacteria, so they grow in a thick, continuous layer:
True
False
The Correct Answer is B
The goal of streaking is to isolate individual bacterial colonies from a mixed or dense culture, not to produce a thick, continuous layer. By streaking a loop across an agar plate in a systematic pattern, bacteria are progressively thinned out, allowing single cells to settle separately. These individual cells then grow into discrete colonies that can be identified, counted, or further studied. Producing a thick, continuous layer would prevent isolation and make it difficult to distinguish individual colonies, defeating the purpose of streaking for isolation and accurate microbiological analysis.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
A. Purple: Purple indicates Gram-positive bacteria, which retain the crystal violet-iodine complex within their thick peptidoglycan cell walls during the Gram staining process. The color persists even after decolorization with alcohol or acetone.
B. Blue: Blue is not a standard color outcome in Gram staining. Gram-negative and Gram-positive bacteria are typically differentiated as purple or pink/red; blue may appear in other specialized staining techniques but not standard Gram staining.
C. Pink/Red: Gram-negative bacteria appear pink or red after Gram staining. Their thin peptidoglycan layer does not retain the crystal violet-iodine complex after decolorization. They are counterstained with safranin, which imparts the pink/red color, allowing differentiation from Gram-positive bacteria.
D. Green: Green is not a result of Gram staining. Green coloration is associated with other staining methods or pigments but is not part of the Gram stain differential process.
Correct Answer is C
Explanation
A. Louis Pasteur: Louis Pasteur is known for his contributions to germ theory, pasteurization, and vaccines, including those for rabies and anthrax. While he advanced microbiology, he did not develop the Gram stain technique.
B. Robert Koch: Robert Koch established the germ theory of disease and developed techniques for isolating and culturing bacteria, including identifying the causative agents of tuberculosis and anthrax. However, he was not responsible for creating the Gram staining method.
C. Hans Christian Gram: Hans Christian Gram, a Danish bacteriologist, developed the Gram stain in 1884. This differential staining technique allows bacteria to be classified as Gram-positive or Gram-negative based on cell wall properties, greatly aiding in bacterial identification and diagnosis of infections.
D. Alexander Fleming: Alexander Fleming discovered penicillin, the first widely used antibiotic, in 1928. While pivotal in microbiology and medicine, he did not contribute to staining techniques such as the Gram stain.
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