First Lab

First checked growth from finger prints:

Hey folks! Today was the second day of lab work and we had a bit of a surprise whilst checking our thumbprint growths. Elizabeth and Hana had beautiful cultures of white growth that showed how bacteria-filled their fingers were before washing, with no bacteria growth on their washed thumb samples. I, on the other hand, experienced profuse growth of bacteria on the unwashed as well as the washed samples of my thumb bacteria. Well, all I can say is that this definitely teaches you the importance of washing your hands well and also restraining yourself from touching your face and hair! – Cecelia

Bacteria growing from our fingerprints

 

Practicing the aseptic technique:

Sterilizing the loop rod.

The aseptic technique is used to inoculate culture media with specific bacteria without introducing contaminating microbes. The first step in this technique is to prepare the work area. After disinfecting the lab table, set up a Bunsen burner, an inoculating loop, and two test tubes. A crucial part of this technique is to sterilize the inoculating loop before and after it comes into contact with bacteria. This is done by holding the loop in the flame of the Bunsen burner until it turns a glowing red and to continue down the length of the rod. Next hold the culture tube in one hand, and the inoculating loop in the other. Using two fingers from the hand holding the inoculating loop gasp onto the lid of the culture tube and take it off. Quickly pass the tube mouth through the flame three times to minimize the chance of dust particles falling into the open tube. Insert the cooled loop into the culture and withdraw a bead of the culture held within the loop. Pass the tube mouth again over the flame three times before replacing the cap. Now it is time to transfer the bead of culture currently on the inoculating loop to another test tube. Pick up the test tube and remove the cap the same way as before and pass the open mouth over the open flame three times. Then insert the loop don into the test tube and roll the handle between your fingers to dislodge the bacteria. Once again pass the open mouth over the flame before replacing the cap. Last but not least, sterilize the inoculating loop
following the directions stated previous. Viola! You have successfully accomplished an aseptic transfer of bacteria! – Elizabeth

Isolation of Bacteria – Part I: Preparation

            Now we actually get to play with bacteria!  Dr. P gave each group of students a culture of bacteria from which we are to grow our own cultures.  We were given mystery bacteria #2 in a slant sample tube.  The bacteria growing on the agar is a pinkish-red color.  So naturally I nicknamed our bacteria “Love Potion.”  (I wouldn’t recommend it for human testing yet).

The mystery bacteria

            A. Preparing a Streak Plate

The first way we will isolate bacteria is through using a streak plate.  A streak plate uses a Petri dish with agar in the bottom.  We first remove some of the bacteria with an inoculating tube and then spread it throughout the top of the agar in the dish.  By spreading the bacteria over the Petri dish in streaks with a back and forth motion of the inoculating loop.  Streaks are spread in four different quadrants of the Petri dish.  Between streaking each quadrant the inoculating loop is sterilized, then the inoculating loop is run back over the last few streaks in the previous quadrant before streaking the next quadrant to spread out the bacteria to have a better chance of isolating the different bacteria when they grow into colonies.  The video below shows Elizabeth demonstrating the technique.

 

            We then placed the Petri dish in the 24 degrees Celsius incubator to allow the bacteria to grow overnight.         

 

B. We also placed some of our mystery bacteria culture in a slanted sample tube to grow a new culture.

C. And finally we placed a sample of our mystery bacteria in a tube of broth to grow an abundant supply of culture. (The more bacteria the merrier, right?) – Hana

 

Tune in next time for the continuation of the mystery bacteria saga!!


Bacteria are living organisms, therefore in order to grow bacteria we must create to proper home complete with proper temperature and nutrients. For temperature there are several incubators in the lab, each at a different temperature. One is at body temperature, 37 degrees Celsius, another at room temperature, 24 degrees Celsius, and the last is outdoor temperature, or around 35 degrees Celsius.  All living creatures need food as well, so there is special dry medium that has all of the special nutrients for our bacteria.  Some mediums are made in to agar and poured into Petri dishes.  The agar for the Petri dishes will solidify into a jello-like substance and make it easier to distinguish individual colonies.  Other mediums are broths that are used for growing bacteria in test tubes. 

The types of dry medium for Petri

A Petri dish with fresh agar.