Final answer:
Microbiologists count bacterial colonies in the range of 30-300 on a plate to accurately determine colony-forming units (CFUs), while plates with more than 300 colonies are marked as TMTC.
Step-by-step explanation:
Microbiologists aim to count plates that have between 30 to 300 well-separated plaques when estimating the amount of live bacteria in a sample, which is quantified as colony-forming units (CFUs). Plates with fewer than 30 colonies (<30) can lead to statistically unreliable results, while plates with more than 300 colonies (>300) can be overcrowded and difficult to count accurately. When a plate is too overcrowded to enable clear counting, it is labeled as having 'too many to count' (TMTC). The ideal range of 30-300 colonies helps ensure that each colony is likely the result of a single bacterial cell, providing a more accurate CFU measurement.