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How to Write Microbiology Unknown Lab Report | Microbiology Lab Paper

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MICROBIOLOGY UNKNOWN LAB REPORT

Unknown Number 118

Jennifer Mills

April 30, 2013

Microbiology, BIO:203.604

Spring/2013

 

INTRODUCTION

In the past, it has been vital to distinguish the identities of microorganisms in the world. Knowing their identity has aided in diagnosing numerous diseases and has discovered the most beneficial treatment.  The purpose of this study was to identify a Gram positive and a Gram-negative bacterium from a mixed culture.  The methods that were previously studied and practiced in the Microbiology laboratory class were applied in order to identity two unknown bacterium.

 


MATRIALS AND METHODS

The lab instructor gave out a test tube labeled number 118, which consisted of two unknown bacteria, one Gram negative and one Gram positive. Sterile techniques were followed while performing precise instructions as stated in the referenced Laboratory Manual.

The first procedure performed to isolate a pure culture from the mixture in the test tube onto a solid media. A sterile inoculating loop collected bacteria from the test tube with the unknown, and streaked a series of zigzag lines along two nutrient agar plates, using the Quadrant Streak Method. These plates were incubated for two days to allow the bacteria to grow. Both plates were studied, noting their characteristics, which were recorded in a journal. One distinct colony grew and a Gram stain was performed on the isolated colony. The Gram stain procedure was carefully followed according to the referred Laboratory Manual. Gram-negative rod shaped bacteria were identified using the microscope. The glass slide and nutrient agar plate were labeled Gram negative and were then stored in the refrigerator. Gram-positive bacteria did not grow. After determining the Gram-negative reaction, specific tests were performed.

In order to identify the Gram-positive bacteria, a sample from the original test tube was streaked on a Mannitol Salt Agar plate and placed in the incubator at 37 Degrees Celsius. There was only one type of bacteria that grew. This was isolated and a Gram stain was performed. Both of the plates were labeled and stored in the refrigerator.  Gram-positive cocci shaped bacteria were identified using the microscope. Several biochemical tests were chosen based on the identification table which was given by the lab instructor. These tests and results were recorded on the flow chart and the tables on the following pages for the Gram-negative and Gram-positive bacteria.

 

Table one and two list the tests, purposes, reagents, observations and results.

All of the following tests were performed on these unknowns:

Gram Positive

  1. Mannitol Salt Agar
  2. Urea
  3. Catalase 

Gram Negative

  1. Simmons Citrate
  2. Mannitol Salt Agar
  3. Gelatin
  4. Galactose 


RESULTS

Unknown number 118 was streaked on a nutrient agar plate. A Gram stain was performed. It was determined that it was a Gram negative rod. Gram positive did not grow. In order to identify the Gram positive bacteria, a sample from the original test tube was streaked on an MSA plate. A Gram stain was performed which identified Gram positive cocci. Table 1 and Table 2 list all of the biochemical tests, purposes, reagents, observations and results. The results are also displayed in a flowchart. 

 

TABLE 1.                                         Gram Negative (-) Tests

TEST

PURPOSE

REAGENTS

OBSERVATIONS

RESULTS

Gram stain

To determine the gram reaction of the organism

Crystal violet, Iodine, Decolorizer,  Safranin

Pink

Gram negative rods

Simmons Citrate

To determine if organism is able to utilize citrate as carbon source

Citrate slant (green)

Color change from green to blue

Positive Simmons Citrate

Galactose

To determine fermentation of galactose

pH indicator phenol red

No color change

Negative galactose fermenter

Mannitol Salt Agar

To determine if it ferments mannitol

pH indicator phenol red

No color change

Negative mannitol fermenter

Gelatin

To determine if it hydrolyzes gelatin

Gelatin tube

It turned to liquid after refrigeration

Positive gelatin test

 

 

 

TEST

PURPOSE

REAGENTS

OBSERVATIONS

RESULTS

Mannitol Salt Agar

To determine if it ferments mannitol

pH indicator phenol red

Medium changed  from red to yellow

Positive Mannitol fermenter

Gram stain

To determine the gram reaction of the organism

Crystal violet, Iodine, Decolorizer, Safranin

Purple cocci

Gram-positive cocci

Urea

To determine if urease hydrolyzes urea

pH indicator phenol red

No color change

Negative urea test

Catalase

To determine if catalase is present

H2O2

Bubbles are present

Positive catalase test

 


DISCUSSION/CONCLUSION

The result of the tests for Gram negative led to the identification of Pseudomonas aeruginosa. A Gram stain discovered that the bacteria were rod shaped. A Simmons Citrate test was performed and the positive result narrowed it down to three bacteria. After a Gelatin and a Galactose test were performed, the only bacterium that remained was Pseudomonas aeruginosa. A negative result on a MSA plate verified this result. This was the correct identification because all of the other Gram negative were eliminated. There were no problems encountered in finding this conclusion.

The result of the tests for Gram positive led to the identification of Staphylococcus aureus. A sample from the unknown bacteria was streaked on a MSA plate. A Gram stain was performed which verified Gram-positive cocci. This was a positive result for mannitol fermentation which narrowed it down to two bacteria. A negative urea test was performed, which also narrowed it down to the same two bacteria.  A positive catalase test verified that the bacteria in the unknown would have to be S. aureus. This was the correct identification because all of the tests performed, identified S. aureus as the unknown Gram positive bacterium. The only problem I encountered was during the isolation streak, Gram positive could not be isolated on a nutrient agar plate.  However, it did grow on a MSA plate and was isolated on a nutrient agar plate.  

S. aureus is a bacterium that is frequently found in the respiratory tract and on the skin. It is a common cause of skin infections, diseases and food poisoning, and is not always pathogenic (Tolan, 2011).  Sometimes, disease-associated strains produce toxins which promote serious infections in the body. These toxins have proteins that activate antibodies which causes resistance. This emergence of resistance has led to MRSA (Methicillin Resistant S. aureus), and is a worldwide problem.

S.aureus was first discovered in 1880 by Sir Alexander Ogston, a surgeon in Scotland.  He saw this bacterium in pus inside an abscess in a knee joint. Twenty percent of the human population are carriers of S aureus, which can be found on the skin and inside the nasal passages. S. aureus is the most common species to cause Staphylococcus infections.  It can cause many illnesses, from minor skin infections, to life threatening diseases such as meningitis, pneumonia, osteomyelitis, endocarditis, toxic shock syndrome, and sepsis (Todar, 2012). It is estimated that some 500,000 patients in American hospitals contract a staphylococcal infection each year.  It is often the cause of postsurgical wound infections and one of the five most common causes of nosocomial infections (Todar, 2012).

 

REFERENCES

  1. McDonald, Virginia et al. Lab Manual for General Microbiology  (BIO 203)
  2. Todar, Kenneth. “Son of Citation Machine.” Son of Citation Machine. Todar, 2012. Web. 19 Apr. 2013.
  3. Tolan, Robert W., MD. “Staphylococcus Aureus Infection.” Staphylococcus Aureus Infection. WebMD LLC., 22 Nov. 2011. Web. 19 Apr. 2013. 

 

 

 

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