Staphylococcus aureus | Microbiology Unknown Paper

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Staphylococcus aureus

UNKNOWN LAB REPORT

General Microbiology

Fall 2013

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INTRODUCTION:

Bacteria exist in millions and contain different properties. The structure of a bacterium can determine its pathogenicity and virulence. Each bacterium reacts differently in different environments. These factors are helpful in diagnosing and treating diseases or producing antibiotics. The methods used in this study are stated in the laboratory manual.(1).

MATERIALS AND METHODS:

The lab instructor assigned unknown. It was previously stated one was gram positive and the other gram negative. To begin, the unknown was inoculated onto a nutrient agar plate using the streak plate method and incubated at room temperature (37 Celsius) in order to grow colonies. One of the two bacteria grew. A gram stain was performed to determine how to grow the second bacteria. A MacConkey Agar plate selects for gram negative which allowed growth. The gram stain confirmed a negative gram reaction.

Further testing was guided by an unknown chart. The chart listed the possible bacteria along with the expected results of each one. To test the ability of the gram positive to ferment mannitol, the bacterium was inoculated onto a Mannitol Salt Agar plate and broth tube. A urea broth tube was also used on this bacterium to be certain about the results. Both tests were recreated twice.

The MacConkey Agar plate also tests for the fermentation of lactose. The ability to reduce sulfur and ferment glucose was verified by stabbing a Kligler Iron tube. Lastly, a test was performed with a urea broth tube as the deciding factor between the last two possibilities for the unknown.

RESULTS:

The gram positive bacterium presented positive results when grown in a Mannitol Salt Agar plate as the color changed to yellow. The urea broth tube also changed to pink indicating the bacterium contained the enzyme urease. After completing both tests twice, the results remained the same.

The Urea broth test caused a color change from yellow to pink. Both Kligler Iron tests resulted in a black color change and a yellow butt.

Table 1 and Table 2 list the test, purpose, and results.

All of the following tests were performed on the gram positive:

Mannitol Salt Agar
Urea
Mannitol broth

All of the following tests were performed on the gram negative:

Kligler Iron
Urea
Hydrogen sulfide

Table 1: Gram Positive Tests and Results

TEST	PURPOSE	REAGENTS	OBSERVATIONS	RESULTS
Gram Stain	To determine the Gram reaction of the bacterium	Crystal Violet, Iodine, Alcohol, and Safranin	Purple circles	Gram positive cocci
Mannitol Salt Agar	To determine the ability of a bacterium to ferment mannitol	None	Plate turned yellow	Ferments mannitol, acidic
Urea Broth Test	To determine the presence of urease	None	Color changed to pink	Breaks down urea
Mannitol Broth Test	To determine the ability of a bacterium to ferment mannitol	None	Color changed to yellow	Ferments mannitol

Table 2: Gram Negative Tests and Results

TEST	PURPOSE	REAGENTS	OBSERVATIONS	RESULTS
Gram Stain	To determine the Gram reaction of the bacterium	Crystal Violet, Iodine, Alcohol, and Safranin	Red rods	Gram negative rods
Kligler Iron Tube Test	To determine if the bacterium can ferment glucose/lactose and its ability to reduce thiosulfate to hydrogen sulfide	None	Black tube with a yellow butt	Reduced thiosulfate to hydrogen sulfide and fermented glucose
Urea Broth Test	To determine the presence of urease	None	Color changed to pink	Breaks down urea
MacConkey	To determine ability to ferment lactose	Bile Salts and Crystal Violet	Growth and color stayed the same	Does not ferment lactose

CONCLUSION:

The results for the gram positive were contradictory. Out of the unknown choices, it was between Staphylococcus aureus and Staphylococcus epidermis. The lab instructor helped to narrow down the remaining bacterium to S. aureus. The bacterium should have been negative for urease and positive for mannitol. A urea broth test identified the gram negative bacterium as Proteus vulgaris. The Kligler Iron tube showed the bacterium was capable of fermenting glucose. The tube became black indicating it could reduce thiosulfate to hydrogen sulfide.

S. aueus is commonly referred to as Staph. It is one of five most common causes of infections that originate in a hospital. The bacterium is non-motile and a facultative anaerobe. It requires oxygen or the production of lactic acid to grow (2). Transmission occurs through sneezing, touching contaminated objects, and saliva. A healthy person can live with this bacteria and not get ill where as a person with an incompetent immune system can suffer life threating illnesses. It can cause minor skin infections such as pimples to blood infections (3). Methicillin- Resistant Staphylococcus aureus (MRSA) is a strain that is resistant to methicillin. Methicillin is designed to be resistant to penicillinase. The rate at which the bacterium evolves has led to alarming healthcare issues.

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