Distinguish between a pure culture and a mixed culture.

Answer

Exercise 4

1. When an agar plate is inoculated, why is the loop sterilized after the initial inoculum is put on?

This is to reduce contamination when it is used again during the second strike. After every inoculum, it should be flamed. 

2. Distinguish between a pure culture and a mixed culture.

A pure culture contains one species of organism while a mix culture contains more than one species of organism.

3. Define a bacterial colony. List four characteristics by which bacterial colonies may
   be distinguished.

A bacterial colony is a cluster of bacteria organisms that grow on the agar plate. Bacterial colonies may be distinguished using four characteristic which are:

• Form that can be circular, irregular, or rhizoid.
• Elevation of the colony that can be raised, convex, umbonate, flat, crateriform
• Margin of the colony that may be entire, curled or lobate.
• Age of the colony

4. Why should a Petri dish not be left open for any extended period?

To avoid airborne contaminants from falling on it. This may cause contamination hence wrong results.

5. Why does the streaking method you used to inoculate your plates result in isolated colonies?

In streak dilution, bacteria are diluted by spreading them apart on the surface of the plate with the loop. In the end, the colonies are spread far apart to form single colonies.

Exercise 5

Pour plate and streaking technique to obtain pure cultures

1. Discuss the relative convenience of pour- and streak-plate techniques in culturing clinical

Streak plate and the pour plate techniques of bacterial isolations are specifically used to get pure cultures of bacteria from the samples.

2. How do you decide which colonies should be picked from a plate culture of a mixed flora?

By looking at the colonies and microscope morphology of colony, I will have to identify I desire to grow mixed cultures of different bacteria and microbes or a pure that has a single strain of bacteria or microbe.

3. Why is it necessary to make pure subcultures of organisms grown from clinical specimens?

For correct identification of the microorganisms and to study the immunological and biochemical properties of the bacteria. This can also be used by the doctors to prescribe the correct antibiotic.

4. What kinds of clinical specimens may yield a mixed flora in bacterial cultures?

Some of the clinical specimen that has the ability to yield a mixed flora are bacterial wound culture. The mixed flora is always brought about when there is contamination which comes from external sources of the wound.

5. When more than one colony type appears in pure culture, what are the most likely sources of
   extraneous contamination?

Contamination can be as a result of use of bear and dirty hands. Some of the contamination can be as a result of contaminated reagents, and when the samples have remained out for a long period, which causes growth with the samples.

Exercise 3: Primary media for isolation of microorganisms

1. Define a differential medium and discuss its purpose.

A differential medium is a culture that is used to differentiate between different organisms based on the appearance of the colony such as shape, color, and pattern. It main purpose it to identify certain bacteria by observing how they ract to the dyes of the mida based on their properties.

2. Define a selective medium and describe its uses

Selective mediu  are culture medium s that allow the growth of specific organism s while inhibiting the growth of others. The medium is used to isolate colonies.

3. Why is MacConkey agar selective as well as differential?

The medium is selective to gram negative bacteria entric bacteria since it has bile salts that are known to inhibit the growth of gram positive bacteria. The medium is laos a differential culture since it has lactose hat differentiate E. coli and salmonella which are which are gram negative lactose fermenters and gram negative non lactose farmenters.

4. Why is blood agar useful as a primary isolation medium?

Blood agar supports growth of any bacteria since it is a nonselective medium and used for primary isolation for both anaerobic and aerobic cultures. In most cases, it is used together with MacConkeys with chocolate agar as the first stage of bacteria identification.  Almost types of bacteria can grow on this medium.

5. What is the major difference between Modified Thayer-Martin (MTM) and chocolate agar? When would you use MTM rather than chocolate agar?

Chocolate agar is a non-selective medium while Modified thayer- martin is a selective medium that is used during isolation of gram-negative bacteria.  MTM should be used when one working with gram-negative bacteria such as Neisseria.