What is a colony-forming unit (CFU)?

A colony-forming unit (CFU) refers specifically to an estimate of viable microorganisms based on colony count. This term is used in microbiology to quantify the number of living cells in a given sample that have the potential to grow into individual colonies under appropriate growth conditions. Each CFU arises from a single viable microorganism that can proliferate to form a colony, thus providing a practical measurement for microbial viability in a sample.

This concept is crucial because it distinguishes between viable cells capable of reproduction and non-viable cells. While other options, such as theoretical quantities of bacteria or measurements of dead microorganisms, do not accurately reflect the living nature of the organisms being counted, the CFU approach focuses solely on living, replicating cells. It's also important to note that CFUs can account for the clustering or clumping of cells, as one CFU may arise from a single bacterium or a group of bacteria that cannot be individually counted under the microscope.

Overall, the CFU metric is widely used in various laboratory and clinical settings to assess microbial concentrations in cultures, food, water, and other samples, emphasizing its importance in microbiological research and diagnostics.