Taking a Pure Culture from the Environmental Samples

The object of this lab was to issolate just one type of microorganism from our environmental sample. Most of the students found many different types of bacteria or mold growing in the Petri dish. Env. Sample #1 was one of the few that had only one or two types of bacteria growing, while Env. Sample #2 had many different microbes growing including mold.  Using aseptic technique we transferred only one strain of the bacteria from our first culture to a second dish to make a pure culture.

A pure culture is made by selecting a single colony that is not touching any other colonies with an inoculating loop and using aseptic technique, transfer the bacteria to a new sterilized Petri dish.  The idea is that it only takes one bacteria to make a culture, and if the colony (the yellowish dots seen in the picture) are not touching any of the other dots, it was made from only one bacteria, and thus it contains only one type of bacteria, or a “pure culture”.

Enviromental Sample #1:
From Lauren's Env.Sample #1 there were a few larger yellow colonies of bacteria that were chosen to become the pure sample bacteria that can be seen in the picture bellow.

Environmental Sample #1 with Large Yellow colony that was selected for the Pure Culture

The colony Lauren chose was very close to all the other bacterial colonies, and therefore very difficult to obtain without being contaminated with the whitish bacteria. As a result I did not end up with a pure culture and had to redo the procedure. This is normal and it often takes many attempts before a pure culture can be obtained. If the culture is given too much time to grow the colonies can grow into one another, making it impossible to obtain a pure culture. In order to ensure a single colony of my yellow bacteria I only touched the inoculating loop to the colony to only pick up a few bacteria, then spread them in wide streaks across a new Petri dish, and only allowed the bacteria to grow in the incubator for a day. The result was much smaller colonies that were not touching. From this I was able to make a pure culture. Bellow is the final yellow Environmental Pure Culture Bacteria sample.

Env. Sample #1 Pure Culture

Env. Sample #1 Pure Culture. In this view you can see how this species forms raised colonies and has a shiny appearance.

Environmental Sample #2:
Kelley's Environmental Sample:

The colony I chose was one of the smallest colonies on my petri dish. It was the only colony of its kind growing on the agar plate and I chose it because of its unique rose color.

The above picture of is of my original environmental swab culture. As you can see, there are many different kinds of bacteria and molds that grew.

Above is my original petri dish (on left) next to my pure culture that I grew from the original (on right)

Above is a closer look at my pure culture. Notice the rose color. It is hard to tell from the picture, but the bacteria is shiny and the colonies are circular. The colony margins are entire and the elevation is convex.