Question

1. What are 4 standard terms used to describe morphological characteristics of colonies growing on an agar plate?

2. Describe the T-streak method

3. Describe which inoculation tool is the most approproiate to use when transfering bacteria from an agar plate to a stab tube.

4. Why is a buffer added to agar? Explain your answer.

5. Look up a growth curve for bacteria growing on an agar plate. Describe why the lag phase occurs.

Answer 1

1. Standard terms used to describe morphological characteristics of microbe colony:

The most standard terms used to describe morphological characteristics of microbe colony are the shape, size, color, transparency and texture. Shape or form it takes while the colony grows - rhizoid, circular or filamentous etc; elevation of the colony viewed from the side of the agar plate - convex, flat or crateriform etc; the shape of the margin of the colony is it lobated, undulated or filiform etc; size of the colony is measured by taking the diameter, color can be described based on the color that appears in the colony like red, white or creamy yellow, texture of the colony if it is smooth, shiny or rough etc. All these are characteristics that would help identify the species of microorganisms.

2. T - Streak method:

Streak plate method is used to grow isolated colonies of the particular microbes.

The name T- streak means three phase streaking pattern. The tool used for streaking usually a loop should be sterile. The loop is made of nichrome or platinum, in some cases it can single time use disposable plastic loop. After the loop has cooled down (by touching on the edge of the sterile agar plate) scoop the microbe to be cultured from the broth mixture. Spread the microbe by dragging the loop in a zigzag manner over one third of the plate. Sterilize the loop after spreading. Turn the plate 90 degrees, drag the loop two to three times over the area just streaked and then drag in zigzag manner over the rest of the plate. Sterilise the loop, turn the plate 90 degrees and repeat the procedure. Always remember not to touch the previously streaked portion while spreading in zigzag manner. After incubation for 24 hours we can see appearance of colonies, the first sector will have more growth but the third sector is the isolated colony of the microbe and there will be less growth in that sector.

3. Inoculation tool most appropriate to transfer bacteria from agar plate to stab tube:

Inoculation needle is appropriate to transfer bacteria from agar plate to stab tube.as it is easier to stab the culture in the tube and is efficient to use for picking the specific bacteria from the agar plate.

4. Addition of buffer to agar:

The reason for adding buffer to agar plate is basically to maintain the pH of the media. SOme bacterial growth can affect the pH and make the media acidic and prevent the growth. Adding buffer maintains the pH of the media, almost near neutral.

5. Lag Phase:

The lag phase in the growing microbe culture is the period when the microbes are active and increasing in individual bacterial cell size but not increasing in number of bacteria. This is for the preparation for the cell division stage by increasing the cell content by producing RNA, enzymes and other molecules.