University of Central Florida (UCF) MCB3020C General Microbiology Lab Midterm Practice Exam

Reducing bacterial concentration using serial dilution is essential primarily to achieve countable colony forming units (CFUs). In microbial studies, particularly when quantifying bacterial populations on agar plates, it is important that the number of cells being plated is neither too high nor too low.

If the concentration is too high, when the sample is plated, numerous colonies will grow too closely together, making it difficult to differentiate individual colonies. This leads to an inability to accurately count the number of colonies formed, which can complicate the estimation of the original bacterial concentration. By performing serial dilutions, you can progressively reduce the concentration of bacteria, ensuring that when a sample is plated, it yields a countable number of distinct colonies. Typically, a range of 30 to 300 colonies is optimal for counting, allowing for accurate analysis and representative results.

While the other options relate to different aspects of microbiological techniques, they do not directly address the specific need for dilution in the context of obtaining accurate colony counts, which is the primary focus of this technique in laboratory settings.