I. STUDY OF BACTERIAL CULTURES (Days 1,2,3)

TABLE 1:

1. How many different colonies are growing on your plate?_____
2. What is a colony? What is unusual about all the bacteria in a single colony?
3. Why is there a reduced risk of bacterial contamination if the lids of agar plates are held above the
      rest of the plate whenever the plate must be opened?
4. How is agar sterilized before use?
5. List two possible sources of error in this portion of the lab.

TABLE 2:

1. How many different colonies are growing on your portion of the plate?_____
2. Did you and your partner produce the same number of colonies?                Explain why it would be      unusual if they were the same.
3. Why was this plate placed in an incubator for 24 hours?
4. List two possible sources of error in this portion of the lab.

TABLE 3:

E. coli “Field” Description

1. What do scientists mean when they describe      the bacteria on this plate as a “field”? 2. Can individual colonies be easily removed from      a field of bacteria? Explain. 3. List two possible sources of error in this      portion of the lab.

TABLE 4:

L. lactis/S. marcescens Streak Description

1. What do scientists mean when they describe      the bacteria on this plate as a “streak”? 2. Can individual colonies be easily removed from      a field of bacteria?                Explain. 3. What is one of the primary purposes of making      streak plates? 4. List two possible sources of error in this      portion of the lab.

5. Would a pipette or a wire loop be more appropriate for:
     a. Placing .2 ml of bacteria onto the E. coli “field” plate?
     b. Spreading the mixture of L. lactis and S. marcescens across the streak plate?
6. If you look at the pipettes used in this lab you would notice a small piece of cotton near their upper      end. Why would there be cotton in the upper tips of pipettes?
7. During the “full” streaking process used with the mixture of S. lactis and S. marcescens how many      times should the wire loop be flamed?
8. During incubation, how should the agar plates be placed?

TABLE #5:

1. What is the purpose of agar in an agar plate?
2. Agar plates are useful for identifying bacteria based on cultural characteristics. List 3 cultural      characteristics used in this lab to identify bacteria.
3. Are these cultural characteristics applied to “fields” of bacteria or “colonies” of bacteria?
4. Why would you guess that agar plates incubated in an inverted position give better results for cultural      characteristics than plates incubated upright?

TABLE #6:

TABLE #7:

II. STUDY OF INDIVIDUAL BACTERIA (Days 4,5,6)
TABLE #8:
SIMPLE STAINING

CHARACTERISTIC	E. coli	L. lactis	Unknown Bacteria
Drawing of Bacteria under Oil Immersion
Shape (bacillus | coccus)
Arrangement (singly | paired | strep | staph)
Cell color

1. What is a bacteria smear?
2. What is the purpose of heat fixation?
3. Why do most stains have a positive charge?
4. What part of the bacteria is stained by the simple stains?
5. List 2 trait you can observe about a bacteria using simple stains.
6. List 3 possible sources of error in this portion of the lab.

TABLE #9:
GRAM STAINING

CHARACTERISTIC	E. coli	L. lactis	Unknown Bacteria
Drawing of Bacteria under Oil Immersion
Shape (bacillus | coccus)
Arrangement (singly | paired | strep | staph)
Cell color
Gram reaction     (+) or (-)

1. How is a differential stain different from a simple stain?
2. Briefly describe the purpose of each of the following chemicals in the Gram staining process.
     a. Primary stain
     b. Counterstain
     c. Decolorizing agent
     d. Mordant
3. What is the most crucial step of the Gram staining process?                          Why?
4. List 3 possible sources of error in this portion of the lab.

TABLE #10:
CHARACTERISTICS OF THE UNKNOWN BACTERIA

Name of the Unknown Bacteria ______________________

1. What does it mean when scientists say to find a known bacteria that “best fits” the characteristics      shown by the unknown bacteria?
2. List the different cell shapes and arrangements studied.
3. List the 2 basic shapes present in bacteria?
4. List at least 3 characteristics can you learn about a bacteria by growing it in an agar plate or agar      tube?
5. List at least 3 characteristics can you learn about a bacteria by staining it and looking at it under a      microscope?