Huge Micro Problem As you know, bacteria are everywhere, invisible to the naked eye, yet influencing every environment on Earth. What happens when you need to know how many individual bacterial cells are contaminating a food, living in an environmental sample, or growing in a culture tube? You need some method for counting the bacteria accurately. But, it is not uncommon for a liquid culture of bacteria to have a billion cells in every milliliter of media. Think about that for one second.

Why Is Serial Dilution Important. Serial Dilution in Microbiology. C dilution requires a substance to be diluted to one part in 1.

In your kitchen, you probably have a teaspoon. Every teaspoon has about 5 milliliters.

That means that every teaspoon of liquid could potentially have 5 billion bacteria in it. Even if you counted one bacteria every second, it would take you over 150 years to get to 5 billion!

Obviously, this is not a viable option. So, what can you do? You need fewer bacteria to count. Orbiter 2010 Shuttle Fleet Download more. Ideally, you want to only have to count between 30 and 300 bacteria, a range of numbers that takes only at most a few minutes to count. But, how do we get there?

Serial Dilution The answer is through dilution. If you simply pull out a smaller, exact quantity of culture liquid, you could count those bacteria and, based on how much you pulled out of the total, you can determine how many bacteria are in your original sample. Sounds easy, right? But first, one more analogy: you have billions of bacterial cells and need to get down to 30 to 300. In order to do that, you would have to dilute your sample about 10 million-fold.

To do this, you would need to take about 15 milliliters of your sample, about 3 teaspoons, and dilute it into your swimming pool! I doubt this is a viable option, especially if you're working in a cramped lab space. So instead, let's not dilute just once.