Ask an Expert - Microbiological Dilutions
Overview
Eurofins Microbiology Laboratories, Inc. is made up of a network of microbiology labs located all throughout the US to support microbiological testing needs. Each lab has dedicated customer support so you get answers fast. Our Ask an Expert Series showcases our scientists from around the country and answers questions customers frequently ask. Videos are published weekly on all of social media platforms.
Ask an Expert Series - Topic #13
Can you tell me more about dilutions used in microbiology assays?
"Precise dilutions are critical step in quantitative microbiology testing such as probiotic enumerations. All methods that involve counting colonies on agar plates specify a “countable range” such as 25 to 250 or 30 to 300 representing the number of colonies allowed to be counted on a plate. This range is statistically determined to reduce variability thereby improving accuracy and to avoid interference or competitive inhibition between colonies. Most samples will be diluted in a series of 10-fold steps and plated across a range of dilutions to increase the chance that at least one dilution will fall in the countable range. We calculate the final count as a colony forming unit per gram or serving from the number of colonies grown on the countable dilution multiplied by the dilution factor." - Andrzej Benkowski, Technical Leader of Eurofins Microbiology Laboratories, Inc. in Madison, WI
