CFU (Colony-Forming Units)

CFU (Colony-Forming Units) are used as a measurement in microbiology to estimate the number of viable microorganisms (such as bacteria or yeast) in a given sample. CFU is important for several reasons: Quantification of Microorganisms: CFU provides a quantitative measure of the number of viable microorganisms present in a sample. It helps researchers and scientists understand the population density and growth potential of microorganisms in various environments. Assessing Microbial Viability: CFU indicates the number of microorganisms capable of forming visible colonies on a specific growth medium under specific conditions. It allows researchers to distinguish viable cells from non-viable or dormant ones, providing insights into the metabolic activity and vitality of microbial populations. Quality Control in Industrial Processes: CFU is used in industries such as food production, pharmaceuticals, and water treatment to assess the microbial quality and safety of products. By determining CFU counts, companies can monitor and ensure compliance with regulatory standards, identify potential contamination issues, and implement necessary measures to maintain product quality. Antimicrobial Efficacy Testing: CFU is employed in evaluating the effectiveness of antimicrobial agents, such as antibiotics or disinfectants. By exposing microorganisms to these agents and measuring the reduction in CFU counts, researchers can assess the ability of the antimicrobial treatment to inhibit or eliminate microbial growth. Environmental Monitoring: CFU counts are valuable for environmental monitoring, such as assessing microbial contamination in air, water, soil, or surfaces. By measuring CFU levels, scientists can identify potential sources of contamination, track changes over time, and develop strategies for mitigating environmental risks. Microbial Research and Studies: CFU counts serve as a fundamental metric in microbiological research, enabling scientists to investigate microbial growth patterns, study factors influencing microbial survival and proliferation, evaluate the impact of environmental conditions on microbial communities, and develop strategies for disease control or biotechnological applications. Problem: You conduct a standard plate count where 50 μL of each dilution is added to each petri plate. The petri plates diluted to 10-2 is a lawn and cannot be counted. The 10-4 diluted petri plate results in 162 colonies. The 10-6 and 10-8 diluted petri plates both had less than 25 colonies on it (so it is not used for the CFU calculation since it is not within 25-250 colonies). Calculate the CFU in cells/mL of the original sample based on these results. Solution # of colonies counted = 162 amount of diluted sample added to the petri plate in mL = 50 μL = mL dilution of the petri plate counted = 10-4 Step 1: Determine the concentration of cells in the diluted sample: (# of colonies counted on the petri plate) ÷ (amount of diluted sample added to the petri plate in mL) = CFU in diluted sample (cells/mL) (162 colonies) ÷ ( mL diluted sample added to petri plate) = 3,240 cells/mL in the diluted sample Step 2: Determine the concentration of cells in the original sample: (CFU in diluted sample) ÷ (dilution of the petri plate counted) = CFU in original sample (cells/mL) (3,240 cells/mL in diluted sample) ÷ (10-4 dilution of the petri plate counted) = 32,400,000 cells/mL in original sample or x 107 cells/mL in original sample CFU = 32,400,000 cells/mL in original sample or x 107 cells/mL in original sample