Which of the following is necessary for a successful streak plate technique in microbiology?

• A. Incubating the plate upside down
• B. Applying a thick layer of bacteria to the entire plate
• C. Adding antibiotics to the agar before streaking
• D. Using a sterile inoculating loop

Answer: (D)

Verified step by step guidance

1. Understand the purpose of the streak plate technique: it is used to isolate individual bacterial colonies from a mixed culture by spreading out cells on an agar surface.
2. Recognize that using a sterile inoculating loop is essential to prevent contamination and to ensure that bacteria are spread properly in successive streaks.
3. Note that incubating the plate upside down is a common practice to prevent condensation from dripping onto the agar, but it is not the key factor for successful streaking itself.
4. Applying a thick layer of bacteria to the entire plate is counterproductive because it prevents isolation of single colonies, which is the goal of the streak plate method.
5. Adding antibiotics to the agar before streaking is a selective technique used for specific purposes, not a general requirement for successful streak plating.