Microbiology Lab Report
Introduction
The science of microbiology is all about microorganisms, what they do and how they work. Microorganisms are ubiquitous, and are a very important part of life everywhere since they have been around for billions of years. The two main themes associated with microbiology are (1) having an understanding of the nature and function of the microbial world, and (2) being able to apply that understanding of the microbial world so that the benefits to the Earth and humans are known(6). This lab specifically does not require the knowledge of what each organism does when introduced to another living organism, like a human. Figuring out the type of bacteria could help with further experiments.
The idea of the unknown bacteria lab is to show …show more content…
the effort it takes to narrow down the list of bacteria through biochemical tests, and to assess how each student uses their knowledge and skills in microbiology. This also shows how successfully each student can inoculate bacteria, and utilize the skills practiced and learned in the previous labs. Materials and Methods
On the first day of lab, the teacher gave each student a test tube.
In each tube a different kind of unknown bacteria was growing on the agar slant. Having the slanted agar allows for more surface area, therefore, more room for bacteria to grow. For each test there is a general set of rules to follow when transferring bacteria from one culture to another.
Disinfect the table surface.
Sterilize the transfer loop using the burner before and after using it to transfer any bacteria at any point in time, the metal should be red hot.
Always pass the top of the tube through the fire after taking the lid off, and before you put the lid back on.
Never set the lids of the tubes or plates on the table when removed for inoculation of bacteria(5).
The first thing to check off the list was the gram stain and the shape of the bacteria. Next, the lab manual gave further specifics for each type of biochemical tests(5). Except for determining the shape and the gram stain, the rest of the tests are on agar plates, in agar tubes, and in broth tubes. The name of each test performed are listed below in the order the tests were done in the lab. …show more content…
Glucose
Sucrose
Lactose
Maltose
MR - VP
Citrate
SIM
Catalase
Oxidase
Nitrate
Starch
Milk
Fat
Urea
Blood Agar
EMB
Mannitol
After receiving the tube with unknown number 29 tapped to the outside, the first thing to do was inoculate the bacteria into one agar slant tube and one broth tube to use the next week for the first set of biochemical tests.
This part is one of the most important things to do correctly. If you don't, you will not have viable bacteria to use for the next set of tests and the whole thing will be ruined. To find whether the bacteria was gram negative or gram positive, there is a specific way to put the bacteria on a slide and stain it so that the color is either pink/red or purple/blue. Finding these two things eliminated the ones on the list that were gram positive and/or were cocci shape, and led to beginning the many biochemical
tests.
Results
The table and chart below show the results of all the tests. The table compares the results of the biochemical tests done in lab with the actual results of the bacteria Citrobacter freundii found from other resources(1). It also shows which of the results were the same for both, helping determine what the unknown bacteria was. The flowchart illustrates the final decision of what the unknown bacteria number 29 was(1&2).
Chart 1
Test
Media
Results
C. Freundii
(actual results)
Results that were similar out of 20 tests
Glucose
Broth tube positive positive
1
Sucrose
Broth tube positive positive
2
Lactose
Broth tube positive positive
3
Maltose
Broth tube positive positive
4
MR
Broth tube positive positive
5
VP
Broth tube negative negative
6
citrate
Agar tube negative positive
-
Motility (SIM)
Agar tube positive positive
7
H2S (SIM)
Agar tube negative negative
8
Indole (SIM)
Agar tube positive positive
9
Catalase
Agar plate positive positive
10
Oxidase
Agar plate positive positive
11
Nitrate
Broth tube negative positive
-
Starch
Agar plate negative negative
12
Casein(milk)
Agar plate positive positive
13
Lipase(fat)
Agar plate positive negative
-
Urea
Broth tube negative N/A
-
Blood agar
Agar plate positive N/A
-
EMB
Agar plate
Growth on plate was purple/pink
N/A
-
Mannitol
N/A
N/A
positive
-
Chart 2
Discussion
Several differential tests were performed on the unknown bacteria number 29. After all of these tests, the list was narrowed down to two different bacteria, Escherichia coli and Citrobacter freundii. When it was looked into further, online and in the textbooks, it was clear that the closest match of the results were with C. freundii(1&2). Out of the 20 different tests that were done C. freundii matched 13 of them, and E. coli matched 11 tests. Of the tests that worked well and had results, some were easier to read like the fermentation tests. A couple were harder to tell what happened, like the EMB test, because the growth was minimal and hard to see. The very last plate test that was done, the mannitol plate, had no growth on it which did not allow for that test to be included in helping figure out the unknown bacteria. Citrobacter freundii bacteria naturally thrives in water, soils, sewage, and food. Their role in the environment is beneficial since they help reduce nitrate to nitrite which is important in the nitrogen cycle. However it can cause, a number of infections in humans. In fact, they are the ones sometimes responsible for infections in the respiratory tract, urinary tract, and blood infections. The symptoms of these are ugly, but luckily the chances are only higher if you have a poor or compromised immune system(4).
Conclusion
In conclusion, I am fairly certain the unknown bacteria I had was Citrobacter freundii. It would have been nice if more of the tests compared the same results, but the C. freundii did match the results for the most tests and also had many similarities to what was read about in the Bergey’s Manual(3). From just knowing the gram stain and shape, the list was not narrowed down by very much. After the first two days of testing I had narrowed it down to three or four bacteria. It wasn’t until after the third set of test that I was able to really narrow it down to two. Finally after the last three plate tests I had enough information to decide that my unknown bacteria was not E. coli, but C. Freundii.
The science of microbiology is all about microorganisms, what they do and how they work. Microorganisms are ubiquitous, and are a very important part of life everywhere since they have been around for billions of years. The two main themes associated with microbiology are (1) having an understanding of the nature and function of the microbial world, and (2) being able to apply that understanding of the microbial world so that the benefits to the Earth and humans are known(6). This lab specifically does not require the knowledge of what each organism does when introduced to another living organism, like a human. Figuring out the type of bacteria could help with further experiments.
The idea of the unknown bacteria lab is to show …show more content…
the effort it takes to narrow down the list of bacteria through biochemical tests, and to assess how each student uses their knowledge and skills in microbiology. This also shows how successfully each student can inoculate bacteria, and utilize the skills practiced and learned in the previous labs. Materials and Methods
On the first day of lab, the teacher gave each student a test tube.
In each tube a different kind of unknown bacteria was growing on the agar slant. Having the slanted agar allows for more surface area, therefore, more room for bacteria to grow. For each test there is a general set of rules to follow when transferring bacteria from one culture to another.
Disinfect the table surface.
Sterilize the transfer loop using the burner before and after using it to transfer any bacteria at any point in time, the metal should be red hot.
Always pass the top of the tube through the fire after taking the lid off, and before you put the lid back on.
Never set the lids of the tubes or plates on the table when removed for inoculation of bacteria(5).
The first thing to check off the list was the gram stain and the shape of the bacteria. Next, the lab manual gave further specifics for each type of biochemical tests(5). Except for determining the shape and the gram stain, the rest of the tests are on agar plates, in agar tubes, and in broth tubes. The name of each test performed are listed below in the order the tests were done in the lab. …show more content…
Glucose
Sucrose
Lactose
Maltose
MR - VP
Citrate
SIM
Catalase
Oxidase
Nitrate
Starch
Milk
Fat
Urea
Blood Agar
EMB
Mannitol
After receiving the tube with unknown number 29 tapped to the outside, the first thing to do was inoculate the bacteria into one agar slant tube and one broth tube to use the next week for the first set of biochemical tests.
This part is one of the most important things to do correctly. If you don't, you will not have viable bacteria to use for the next set of tests and the whole thing will be ruined. To find whether the bacteria was gram negative or gram positive, there is a specific way to put the bacteria on a slide and stain it so that the color is either pink/red or purple/blue. Finding these two things eliminated the ones on the list that were gram positive and/or were cocci shape, and led to beginning the many biochemical
tests.
Results
The table and chart below show the results of all the tests. The table compares the results of the biochemical tests done in lab with the actual results of the bacteria Citrobacter freundii found from other resources(1). It also shows which of the results were the same for both, helping determine what the unknown bacteria was. The flowchart illustrates the final decision of what the unknown bacteria number 29 was(1&2).
Chart 1
Test
Media
Results
C. Freundii
(actual results)
Results that were similar out of 20 tests
Glucose
Broth tube positive positive
1
Sucrose
Broth tube positive positive
2
Lactose
Broth tube positive positive
3
Maltose
Broth tube positive positive
4
MR
Broth tube positive positive
5
VP
Broth tube negative negative
6
citrate
Agar tube negative positive
-
Motility (SIM)
Agar tube positive positive
7
H2S (SIM)
Agar tube negative negative
8
Indole (SIM)
Agar tube positive positive
9
Catalase
Agar plate positive positive
10
Oxidase
Agar plate positive positive
11
Nitrate
Broth tube negative positive
-
Starch
Agar plate negative negative
12
Casein(milk)
Agar plate positive positive
13
Lipase(fat)
Agar plate positive negative
-
Urea
Broth tube negative N/A
-
Blood agar
Agar plate positive N/A
-
EMB
Agar plate
Growth on plate was purple/pink
N/A
-
Mannitol
N/A
N/A
positive
-
Chart 2
Discussion
Several differential tests were performed on the unknown bacteria number 29. After all of these tests, the list was narrowed down to two different bacteria, Escherichia coli and Citrobacter freundii. When it was looked into further, online and in the textbooks, it was clear that the closest match of the results were with C. freundii(1&2). Out of the 20 different tests that were done C. freundii matched 13 of them, and E. coli matched 11 tests. Of the tests that worked well and had results, some were easier to read like the fermentation tests. A couple were harder to tell what happened, like the EMB test, because the growth was minimal and hard to see. The very last plate test that was done, the mannitol plate, had no growth on it which did not allow for that test to be included in helping figure out the unknown bacteria. Citrobacter freundii bacteria naturally thrives in water, soils, sewage, and food. Their role in the environment is beneficial since they help reduce nitrate to nitrite which is important in the nitrogen cycle. However it can cause, a number of infections in humans. In fact, they are the ones sometimes responsible for infections in the respiratory tract, urinary tract, and blood infections. The symptoms of these are ugly, but luckily the chances are only higher if you have a poor or compromised immune system(4).
Conclusion
In conclusion, I am fairly certain the unknown bacteria I had was Citrobacter freundii. It would have been nice if more of the tests compared the same results, but the C. freundii did match the results for the most tests and also had many similarities to what was read about in the Bergey’s Manual(3). From just knowing the gram stain and shape, the list was not narrowed down by very much. After the first two days of testing I had narrowed it down to three or four bacteria. It wasn’t until after the third set of test that I was able to really narrow it down to two. Finally after the last three plate tests I had enough information to decide that my unknown bacteria was not E. coli, but C. Freundii.