When looking at our dipslides, people often ask us which one they should get. “What agar should I use?” “What does each agar grow?” “What is best for my application?” Like many of our answers to your questions, it really depends on the application and the results you are trying to achieve. But to help you make a decision, we’re going to take a closer look at each of the agars we offer. Today, we’re looking at Tryptic Soy Agar!

A Brief History

In 1955, Tryptic Soy Agar was revealed by Leavitt to support hearty growth of aerobic and anaerobic microorganisms. Tryptic Soy agar is a general purpose medium, an enriched media suitable to support fastidious heterotrophs. There are several versions of Tryptic Soy agar with various additives that can enhance the medium. The most commonly used supplemented form is Lethicin and Tween, which is widely used in environmental monitoring. Our Tryptic Soy agar does not contain any additives, and is simply used as a general purpose medium.

The media contains soybean meal and casein enzymatic digest, which is why it supports such wide growth. The digests supply nitrogen in the form of amino acids and polypeptides, which is a great nutrient source for microbes. The media also contains sodium chloride to maintain the osmotic equilibrium. It’s a fairly simple formulation, which is why additives are sometimes used to make it more selective.

Growth

tryptic soy agar, dipslides, dipslide, tryptic soy dipslideIn our experience, Tryptic Soy agar is commonly used in educational settings where a wide variety of microorganisms can be supported. In addition, we have found it used in cosmetic testing, water and wastewater applications, and food testing. It is also frequently used as to maintain cultures.

Tryptic Soy agar is cream or off-white in color. It does not contain any dyes that are taken up by the microorganisms growing on it. If you check out some of the growth images on our expanded technical document, you’ll see many of the colonies are transparent.

We combine Tryptic Soy agar on a dipslide paddle with Rose Bengal agar on the other side. These media are very complementary to each other. While Rose Bengal agar supports the growth of yeasts and molds and inhibits bacteria, Tryptic Soy agar supports bacterial growth, along with yeast and mold growth.

Incubation

Tryptic Soy Agar is best incubated at 30-35°C and examined for growth after 48 hours. It may need to incubate longer, but it is best to check at 48. Because TSA agar supports such fastidious growth, it can become overgrown and confluent more easily than some other media. If incubating at room temperature, it should be left for at least 5 days, up to 7 days.

Here’s where incubation can get tricky when using a dipslide that has two uniquely different media. The optimal incubation temperature for bacterial growth is typically more like 35 ± 2°C for just 24-48 hours. Yeasts and molds, on the other hand, prefer lower incubation temperature for a slightly longer period. So how should you incubate?

Well, if you’re focusing on the molds, lean more towards the lower temperature and 48 hour incubation period. If you’re focusing on the bacteria, lean more towards the higher temperature and 24 hour incubation period. If you want to focus on both simultaneously, focus on the middle of the range, somewhere around an incubation temperature of 32-33°C with a first check at 36-48 hours. This is why we recommend a range of 30-35°C.

Check out our technical document for more information on our Tryptic Soy dipslides, or to view a microbe identification chart with images of microbes grown on Tryptic Soy agar.

That’s it for today’s micro-lesson. Hopefully, you now have a better understanding of how Tryptic Soy agar works and what microbes it’s best used for.