Study Guide to Help with
Laboratory Exam 1
Microbiology 1214
A partial study guide only. Not intended to replace the review sheets or the “Know the following” sections on your labs.
These slides are not presented in any particular order.
Name this
Procedure
Identify the two types of bacteria present by shape and gram stain.
In a gram stain what is the primary stain?
The mordant? The counterstain?
How does this differ from a simple stain?
Identify the shape and gram stain of the bacteria present in this gram stain.
Identify the shape and gram stain of the bacteria pictured. Think on this one!
Name the gram stain and shape of the bacteria pictured.
Name the genus of the organism pictured.
Note the size when determining the
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This plate was made from a swab obtained from the bottom of a shoe.
Can you differentiate between bacteria and fungi?
How do we tell the two apart?
This technique is performed after my smear has dried. What is the name of this technique?
Give two reasons why it is performed?
If I am doing a gram stain and leave out the mordant, what color will all of my bacteria end up being?
Identify this stain procedure.
What are we looking for with this stain?
The presence of a capsule increases the __________ of the bacterium.
What composes a capsule?
What staining procedure is this?
What are the green structures?
What type flagella is pictured?
Why do we use oil on the oil immersion objective?
Because it has the same _______________
_______________
as glass.
What is the proper method of storing a petri dish in an incubator. Give two reasons why it is important to store by this method.?
By the way:
• Name some acid dyes, some basic dyes.
• An acid dye stains the _____ while a basic dye stains the _____.
• Given a staining procedure be able to tell me whether a dye used in it is acidic or basic. • Name a gram negative bacteria studied in lab. • Name a gram positive bacteria studied in lab. Bacteria or
Fungus?
Identify the hemolysis indicated by the arrow.
Identify the hemolysis at the arrows.
Identify the shape of the bacteria pictured at the arrows. (It isn’t bacillus!)
Assuming we are on oil, what is the size of one coccus of the
There are many reasons for identifying an unknown bacterium. The reasons range from medical purposes, such as determining if the unknown could cause ailments in living things or knowing what microorganisms are needed to make antibiotics. The experiment was done by applying methods in order to identify an unknown bacterium.
The colonies were smooth, translucent, and had a white brownish color. The Gram stain resulted in Gram positive cocci. After the Gram stain was completed, the bacteria were streaked on a Mannitol-Salt Agar plate and a Catalase test was performed. After these test were completed a Phenol Red Dextrose Fermentation tube was inoculated, and a SIM Tube inoculated.
2) Record the shape of the bacteria, the arrangement of the bacteria, and the gram staining characteristics.
If new crust is indeed being produced at the rifts, where does the additional older crust go?
Table 3 shows Gram stain results that indicated C. Freundii as a gram negative bacterium in rod shapes scattered in singles and some in pairs. Each gram stain produced the same results. The Bartholomew and Mittwer method of endospore staining indicated that C. Freundii tested negative for endospore formation. Table 4 shows the biochemical test results of the unknown and the official test results for comparison.
To perform this test, a tube of broth rich with glucose is acquired. In this tube is phenol red, a pH indicator. Initially, the tube appeared pink in color, indicating a normal pH level. Next, a sample of unknown #44 is introduced into this medium using the aseptic technique, and this is allowed to sit for several days. If the organism is able to ferment glucose, the pH in the medium would decrease and cause the phenol red to exhibit a yellow color. In addition to the straw color, gas can also be produced and trapped inside the Durham tube placed in the medium. This production of acid and gas is a direct result of the fermentation of glucose, as seen with unknown
1. (10 points) Write out your pre-lab prediction, including what evidence or previous knowledge you have to support that prediction.
Preliminary studies help identify Genus species of bacteria. Two different preliminary study pathways must be used since two different pathogens were found in the sample. A dilution and a quadrant streak are the ideal methods to separate pure cultures of bacteria. MacConkey Agar and CAN (MAC) is a selective media that is used for the cultivation of gram negative bacteria. (PEA) is a selective media that is used
For the temperature test each bacteria was placed on a nutrient agar and incubated for either 10, 20, 30, 40, or 50 degrees Celsius for 48 hours. During the pH test, each organism was placed on four agars varying in pH level from pH 2, 4, 6 and 8 and incubated near 37 degrees Celsius for 48 hours. For the osmotic pressure test, each organism was placed on four agars one each containing 2%, 5%, 8%, and 11% NaCl concentration levels. These were incubated near 37 degrees Celsius for 48 hours. The results of the tests are recorded in Tables 1, 2, and 3. All tests were performed according to the instructions provided in Leboffe & Pierce(1). The biochemical tests used on both unknowns and the ubiquity are:
The drops of crystal violets, approximately 15 drops, were flooded until the smear were all covered and then allowing resting for one to two minutes. After two minutes, the slide was titled over the sink and washed off, with the distilled water bottle, by aiming the stream of water above the smear. The specimen appeared blue-violet when observed with the naked eye. The drops of Gram’s iodine were applied on the slide until covered and then allowed to react for one minute or more. After the time elapsed, the slide was rinsed again with distilled water following immediate drops of Gram stain decolorizer added one drop at a time.
The purpose of this experiment is to distinguish and indentify an unknown bacterium. There are several tests that can help one eliminate and narrow down the options. The most useful test, and the very first one done, is a gram stain. This test will tell whether the bacterium is gram-positive or gram-negative. After the type of gram stain is identified, the tester has a wide array of differentiating tests at their disposal. Based on the results from these tests, and the numerous others that are available, one can accurately establish the identity of an unknown bacterium.
Figure #1 This picture show the gram stain of unknown #3. The image is under 1000x magnification using oil immersion technique. Gram (-)
Escherichia is a genus of aerobic gram-negative rod-shaped bacteria of the family Enterobacteriaceae that form acid and gas on many carbohydrates, such as dextrose and lactose, but not acetone, which include occasional pathogenic forms, including some strains of E. coli which are normally present in the human intestine as well as other forms which typically occur in soil and water (Webster). Escherichia coli is a gram-negative bacilli that rarely varies in shape and size and when stained often resemble safety pins because the ends of some bacilli stain more densely than does the middle; which is a characteristic called bipolar staining which is common in enteric gram-negative bacilli (ASM). Gram negative cells have a thin cell wall layer and will stain red to pink. The staining process is the same as Gram positive, requiring four steps: applying a primary stain, adding a mordant, then rapid decolorization and completing with a counter stain. Applying the alcohol for decolorization dissolves the outer membrane and leaves small holes in the thin peptidoglycan layer through which the crystal violet-iodine diffuse. The gram-negative bacteria is colorless after the decolorization; therefore adding safranin
All three slides were observed microscopically and macroscopically. Microscopic observation of LB tubes 1 and 2 after simple staining presented bacterial growth. Milk tube #1 was gram positive with bacterial growth of streptococci and streptobacilli. Milk tube #2 was gram positive with diplococci and streptococci bacteria. As shown in table 2, macroscopic observations, included, texture, color, odor, pH and additional observations. All three tubes presented different results, however, there was no visible changes in tube 3 (control).
The purpose of this experiment is to obtain isolation of individual species of particles from the mixed culture. This is completed through the isolation technique of streak plate. The objective of this experiment is to replicate the technique of streak plate but on a much larger scale. Because it is on a larger scale the particles are able to be visually observed as they are isolated using the streaking technique as the experiment is conducted. The benefits of the streaking technique is when a cultures has multiple species they are able to be more easily identified once they have been isolated. This experiment is much like the experiments completed on an agar plate but on one a much larger scale and where techniques