Lab 2 Results

Prelab Activity:

Serratia marcescens cultivated on trypticase soy agar

Serratia marcescens cultivated on trypticase soy agar

This colony appears to round, have an entire margin, and an umbonate elevation. The color is a deeper red in the middle and gets lighter towards the outer edge. The colony appears to be dry, is also very shiny and slighly translucent towards as the color gets lighter along the edge.

Streptococcus salivarius cultivated on Mitis-salivarius agar

Streptococcus salivarius cultivated on Mitis-salivarius agar

This colony is round in shape and has an entire margin. The elevation is pulvinate and the texture appers to be moist because the colony is shiny. The color of this colony is a very dark black, we think of it as looking like a pupil of an eye.

Unknown isolate cultivated on trypticase soy agar

Unknown isolate cultivated on trypticase soy agar

This colony is irregular in shape and seems to have a undulate margin. The colony appears to be moist as it is very shiny. The color is white in the middle and becomes opaque around the outer edge. It is hard to tell by the picture if the colony is flat or slighly umbonate. The middle is darker in color than the outer edge, which could cause the middle to appear raised even though it may be flat.  

 – Tara Aubry & Anneliese Cornejo





Lab Area for Tara Aubry and Anneliese Cornejo










Lab #2

Exercise #1

On September 27th 2010, Tara Aubry and I drew a black line on our Nutrient agar plates and exposed half of the plate to the air for a 30 minutes. With our other half of the agar plate we used a moist sterile cotton swab and wiped the surface of our lab area. After contaminating our cotton swabs we gently streaked the agar plates and carefully shielded the plate against airborne contamination. When the 30 minutes was up, we put the lid back on and inverted the plates. We placed it in our incubator at 34.4 degrees Celsius.

After 48 hours of incubation time we observed the agar plates to find bacterial growth. The bacteria on the left side had a small colony on the side we swabbed from our labs surface The colony was slightly irregular, raised and shiny. The bacteria on the right side had a really big colony on the airborne side that was round, flat, white and moist.

Annelieses Agar Plate


We came to the conclusion that the picture on the left side did not get exposed to a lot of the dirt on the cotton swab. And the bacteria on the right was contaminated with airborne pathogens.

We are wondering why the bacteria on the right did not form any colonies from the cotton swab. We both swabbed the same area of our lab surface but got different results.

Excersise #2

After we finished exercise #1, we cleaned up our area and laid out the supplies that were needed for exercise #2. We first lit our candle so that we would have a clean flame once we needed to sterilize our inoculating loops. In our left hands we had one agar slant of the Serratia marcescens bacterial culture and one TSB tube (Tryptic Soy Broth). We made sure to hold both the agar slant and TSB tube at an angle to limit airborne contamination before we removed the caps. Once the caps were removed, we heated up the end of our inoculating loops in the flame of the candle until they glowed orange. As per the instructions we let the loops cool down for 30 seconds before placing it on the S. marcescens agar slant. After the 30 seconds we placed the hot loop on the agar and heard a sizzle sound. Then we scraped a small amount of the S. marcescens with the end of our sterile loops and transferred it into the TSB tube. Using a swishing motion we released the S. marcesens into the TSB tube and then placed the cap back on. Once the cap was on the TSB tube we sterilized our inoculating loops again and prepared a second TSB tube in the same manner the TSB tube with the S. marcesens. However, before placing the cap on the second TSB tube we had to add E. coli. We added the E. coli exactly the same way the S. marcescens was added to the TSB tube. We did this by sterilizing our inoculating loop, letting it cool, scraped a small amount from the agar slant, and then transferred the E. coli by swishing it the broth. We then labeled both broth tubes with the date and species of bacteria. Finally the tubes were placed in a cup inside our incubator at 34° C.

After letting the bacteria incubate for 48 hours we observed both tubes for bacteria growth. Both the S. marcescens and E. coli tubes had white cloudy sediment at the bottom. In addition, the broth itself was cloudy too.

This is what our bacteria looked like after 48hrs.

Anneliese Tube

Tara's Tube

Excersise #3

Tara's agar plate


We  took a nutrient agar plate out of our box and placed it on our lab surface. Then got out our TSB tube of E. coli and S. marcescens  and put it down next to the agar plate. We drew 4 quadrants on the back of our agar plate so we could use the streak technique with our bacterial mixture. We held our loop over a candle until it started to glow orange and let the loop cool for 30  seconds. We dipped our loop in the broth suspension to get a drop of the bacteria. Then we carefully held the lid over the agar plate while we gently inserted the loop onto the agar plate. We used the streak plate technique on quadrant one and removed the loop to put it over the candle again. We did this process for all the sections of the agar plate. We inverted the plate and incubated it for 48 hrs at 37 degrees Celsius.

Anneliese's Agar Plate
Anneliese’s Agar Plate – S. marcescens and E. coli – October 1, 2010


Tara’s seemsed to have more of the S. marcesense colonies, which in the streak plate were round, majority were slightly raised and a few were flat, the color ranged from light red to very dark red. In area and 1 and 2 there appeared to be a few colonies of E. coli, which were white, irregular, and flat.

Anneliese’s streak plate was the opposite in which the majority of colonies were E. coli and there were very few colonies of S. marcesense. Most of her colonies were white, irregular, and flat.  

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