How do you determine colony forming units (CFU)?

CFU determination quantifies viable microorganisms through plate counting. The process involves: serial dilution of sample (typically 10-fold dilutions), plating appropriate dilutions on agar (spread plate or pour plate), incubation under optimal conditions, and counting colonies (ideally 30-300 per plate for statistical validity). CFU/mL = colonies counted / (dilution factor x volume plated). Proper technique requires: adequate mixing between dilutions, appropriate incubation time, and counting plates with countable numbers. CFU only counts cells capable of forming visible colonies, potentially underestimating total viable count. Alternative methods include most probable number (MPN) for low counts and flow cytometry for rapid enumeration.