Determining the number of viable bacteria or fungal cells in a sample, expressed as colony forming units per milliliter (CFU/mL), is a fundamental microbiological technique. This quantitative assessment involves serially diluting a sample, plating known volumes onto growth media, incubating under appropriate conditions, and subsequently counting the resulting colonies. The number of colonies is then multiplied by the dilution factor to arrive at the concentration in the original sample. For instance, if 50 colonies are observed on a plate inoculated with 0.1 mL of a 10-5 dilution, the concentration in the original sample is calculated as 5 x 107 CFU/mL.
Quantifying viable cell counts is critical for various applications, including assessing water and food safety, monitoring the efficacy of antimicrobial agents, and controlling fermentation processes. Accurate enumeration provides essential data for research and development, quality control, and regulatory compliance. Historically, this process has been a cornerstone of microbiology, enabling scientists to understand microbial populations and develop strategies for their management.
