UV Light

The UV wavelength has the unique property of being able to kill microorganism. This really cool feature is being studied scientists and in some hospitals they use UV lights as a sterilization method to clean hospital rooms after a sick patient leaves. However, UV light is also known to cause mutations, and so in a hospital setting only the longer UV Light C wavelength us used just in case someone was to walk in the room by accident.

UV Light bulb and Petri dishes undergoing sterilization.

In Lab we decided to see if this was true and if UV light would kill or retard the growth or our bacterias. Everyone made a carpet spread of bacteria on a Petri dish. Since UV light is blocked by any physical barrier except air, to conduct the experiment we simply covered half the Petri dish with paper, and exposed each dish to one minute of UV light. Oh, and remember to take the glass lid of the Petri dish because that will block UV light too! Next lab we checked the dishes and found that there was still bacterial growth on the UV treated side of the plates, but it did seem to be a little less growth then the non-UV light treated side. We thought that maybe the experiment did not work very well because we set the wave length on too low a setting. No one checked the setting before we began.

Making Yogurt!!!

Today we get to apply what we learned about microbes to the real world - or rather the kitchen -- because we are going to make yogurt and Kefir!

The process was really simple. We start out with whole milk and boil it in the microwave to kill any pathogens. Then we filled two insulated cups and added a spoonful of yogurt to one and kefir to the other, mixed well, and let sit over night in a warm incubator. Another method would be to leave it in a stove with the light one. The light will provide just enough heat for the microbes to grow. Next the cups had turned from liquid to a solid cup of yogurt and a creamy cup of kefir! Most the students that tried them agreed it was good but a little sour. Just add a little sugar and berries and you have you're own homemade yogurt!

Sweet way to mix yogurt : )

Finished yogurt & kefire ready to eat!

Disclaimer: If you try this at home and get sick it's not my fault : )

Oxidase Test

Performing an oxidase tests lets us see if our bacteria have cytochrome oxidase, as participant in electron transport during respiration. To check, we simply take the old unknown bacterial plate we used to the antibiotic test and a vial of oxidase. It it turns blue right away the test is positive, but if it does not turn blue or turns blue after 30 seconds then the test is negative. Our plate only turned a little blue after a few minutes indicating that our unknown bacteria is NEGATIVE for Oxidase.

Negative Oxidase Results

We also added hydrogen peroxide to the plate to see if it would react and our bacteria fuzzed a lot! This means our bacteria can use aerobic respiration.

Results of Protien-Indole, Citrate, Nitrate, and Urea.

Protien-Indole Results: Negative. When we added the Kovak's solution after 48 hours, the broth did not turn red. Therefore our bacteria does not have the ability to use tryptophan as an engergy source.

Protien-Indole Restults: Negative

Citrate Results: Negative. Our slant had a tinge of blue on top, but the rest of the tube remained green. Therefore our bacteria does not use citrate.


Protien-Indole Results: Negative


Nitrate Results: Positive. When we added the A&B solution nothing happened. Then we added the zinc dust nothing happened either. If no change occures when the zinc dust is added after ten minutes, then the test is positive for nitrate reduction and nitrite ions are present.

Nitrate Results: Positive

Urea Restults: Negative. Our bacteria does not have the enzyme that breaks down urea because the test tube turned yellow. If the tube remained red it would indicate a positive result.

Urea Restults: Negative

Reading the Results of our Antibiotics Test

Upon retrieving our antibiotic test from the incubator, we saw the following...

We measured the diameter of the clearing around each of the antibiotics used to determine the sensitivity of our bacteria to each antibiotic. We found...

• Penicillin: 27mm--sensitive
• Vancomycin: 22 mm--sensitive
• tetracyclin: 25 mm--sensitive
• Erythrocyclin: 31 mm--sensitive
• Chloromphenicol: 30 mm--sensitive
• Neomycin: 20 mm--sensitive

In conclusion, our bacteria is VERY sensitive to a lot of antibiotics...yet another distinguishing characteristic!