Question

Understand why, when using solid media, the inoculum is serially diluted on the slide.

A) To ensure the slide doesn't break due to excess bacterial growth
B) To speed up the bacterial growth process
C) To create a range of bacterial concentrations for different experiments
D) To observe the shape of bacteria more clearly

Answer 1

The inoculum is diluted serially on solid media to create a range of bacterial concentrations that allow for the counting and isolation of distinct bacterial colonies, essential for various experiments and identification processes.

Step-by-step explanation:

When using solid media, the inoculum is serially diluted on the slide to create a range of bacterial concentrations for different experiments (option C). This procedure is essential for achieving plates with colony-forming units (CFUs) in the viable count range of 30-300. The serial dilution is performed by adding a fixed volume of bacterial cells to a dilution solution, then using this dilution as an inoculum to create consecutive dilutions. By doing so, one can control the number of bacteria spread on each agar plate, ensuring isolated colonies are distinct enough to be counted, without being too numerous to count or too sparse for a valid assessment.

Cultures grown on solid media, such as agar plates, demonstrate colonial characteristics which can be used to identify and separate bacteria in a mixed culture. Through the streak plate method, a single type of bacteria can be isolated from a sample containing multiple species. Each colony on the agar plate is derived from a single bacterial cell, and as these cells reproduce, they form a visible colony composed of clones.