Experiment 4 Bacterial Growth And Sterile Techniques

EXPERIMENT 4 BACTERIAL GROWTH AND STERILE TECHNIQUES

1. INTRODUCTION AND AIM It is very important that in biology to study with pure cultures. To make them pure sterile techniques are used, if not the culture will be covered microorganisms. Some of these microorganisms called contaminating microorganisms may grow faster than cultured cells. In this sense contamination is the act of contaminating or polluting; including (either intentionally or accidentally) unwanted substances or factors. So we use it to make our cultures pure. Bacteria grow very fast. In ideal circumstances some bacterial cells can divide and double every 20 minutes. There are 2 types of medium that bacteria are grown; solid or liquid. A culture medium contains substances which enable bacteria to live and grow. A solid medium contains also agar which is made from sea weed. A solid medium that is incubated at 37oC for all day will allow a microorganism to grow into colonies which can be seen with naked eye. In this experiment the culture of Escherichia coli was used.

2. MATERIALS AGAR PLATE

BUNSEN BURNER

GLASS ROD

COTTON SWAB

LB

MEDIUM

INOCULATION LOOP

TIP

MICRO PIPETTE

3. METHODS A. Streaking Streaking is a technique that used in microbiology to isolate a pure tension from a single species of microorganism, often bacteria. There are some components to streak the culture. These are agar plate, loop, and Bunsen burner. The procedure is described below step by step; o First of all platinum part of inoculation loop must be seared until it becomes reddish. o Before dipping it bacterial culture it is cooled in the air for a short time or stabbed into sterile agar. o After cooling, loop dipped into liquid bacterial culture then, bacteria on the loop are streaked onto a small part of agar plate. (Step 1) o Again loop is made sterile by flaming and then the methods written in the first step are applied except dipping loop into liquid bacterial culture. A little bit bacteria which are streaked first is taken and streaked to the fresh part of the plate by perpendicular to first part. It is done for separating the bacteria from each other to observe in more detailed (Step 2) o And finally, third time methods are applied in the second step. This time less concentration of part is acquired. It is waited under 37 centigrade degree for one day.

B. Contamination I applied the cotton swab to the trash can, then I spread it to agar plate. It is waited in 37oC for one day. C. Spreading Spreading is a technique that used to separate the colonies from a culture. The culture is firstly serially diluted as 1:000, 1:10000, and 1:100000 each in 1ml of liquid medium from the LB Medium solution. How spreading technique is used explained below;

Micro pipette glass rod, tip, Bunsen burner and 95% ethanol were used in this experiment.

o Begin with, 50 micro liters each concentration of cultures are taken with the micro pipette and tips, spread them separated agar plates. Use a new tip for each.

o Then disinfect the glass rod firstly by dipping the 95% ethanol then flaming. Be careful about not to kill the bacteria in the agar plate. So first cool the glass rod in the air and touch it the sides of plate to make it cooler.

o After cooling, glass rod is slid up and down in the agar plate, at the same time the plate is rotated with a hand.

o At the end of the spreading, plates are waited in 37oC for one day.

4. RESULT A. Streaking

B. Contamination

C. Spreading

5. DISCUSSION A. Streaking

B. Contamination

C. Spreading

6. REFERENCES http://www.colorado.edu/ http://content.answers.com http://www.science.siu.edu