Aseptic Technique and Isolation of Bacteria

A. Aseptic Technique

1. What is the purpose of flaming the mouth of the tube?

Passing the mouth of a tube through the flame of a Bunsen burner creates a convection current which forces air out of the tube. This kills the microbes at the mouth and prevents airborne contaminants from entering the tube.

2. What is the primary use of slants?

Slants are for long term retention , they provides a deep layer of nutrients longer than a plate and won't dry out as easily , and they are easier to store and transport .

3. Can you determine whether a broth culture is pure (all one species) by visually inspecting it without a microscope?

No , naked eye can not determine between different species .

4. What is the purpose of flaming the loop before use? After use?

To kill all contaminating organisms, thus sterilizing the loop .

5. Why is aseptic technique important?

Proper aseptic technique prevents contamination of cultures from foreign bacteria inherent in the environment and to maintain pure stock cultures while transferring cultures to new media .

B. Isolation of Bacteria by Dilution Techniques

1. Why should the plates be incubated in an inverted position?

To prevent water which condenses on the lid drop onto the culture and make the colonies of bacteria spread together.

2. Could some bacteria grow on the streak plate and not be seen using the pour plate technique? Explain.

Some obligate aerobic organisms will not grow in a pour plate as there’s lower level of oxygen in the agar .

3. What is a contaminant? How would you determine whether a colony was a contaminant on a streak plate?

A contaminant is an unwanted microorganism . A contaminant might appear different from the majority of colonies and often grow off the streak line.

C. Special Media for Isolating Bacteria

1. How did the results observed on the MSA and EMB correlate to the Gram reaction of the bacteria?

MSA prohibits the growth of bacteria unable to tolerate...