The Results! Gelatin and Fermentation

Welcome back!  The moment we have all been waiting for!  What happened with all those tests from earlier this week? Does our bacteria feast on Gelatin? Does it ferment glucose? Let's see!

Gelatin Hydrolysis Test:


Recall from last time, we used aseptic technique to inoculate our sample in a medium composed of gelatin and placed it in an incubator.  After 48 hours we immediately placed the sample into the refrigerator for 15 min.  After, retrieving the sample, we had to check for liquifaction by tilting the tube slightly.  If "F" has the enzymes to consume gelatin, the sample would remain liquified once cooled.  Let's see!

The Results:

Because the gelatin remains intact, "F" does not have the enzyme gelatinase; our Gelatin Hydrolysis test is negative.

Fermentation of Carbohydrates:


Recall, last time we inoculated three broth tubes: one containing sucrose, one containing lactose, and one with glucose.  After 24 hours we recorded the results!

The Results:

Above: Sucrose

Above: Lactose

Above: Glucose

From Left to Right: Sucrose, Glucose, Lactose

Remember from before all the tubes were a red color.  Fermentation of the sugar resulted in a color change due to a pH indicator added to the broth.  It is hard to notice, but there is also a Durham tube located in each tube.  We had no bubbles in these tubes; therefore, our bacteria does not produce gas as an end product to fermentation.  However, "F" ferments glucose and lactose, producing acid as an end product.  This is indicated by the yellow color found in glucose and the orange color found in lactose.  Our bacteria does not ferment sucrose.

Triple Sugar Iron Agar Test (TSIA):


Recall, we used the aseptic technique to inoculate an agar slant containing triple sugar iron agar (consisting of  1% lactose, 1% sucrose, 0.1% glucose).  After incubating for 24 hours, we examined our slant!

The Results:

The slant was determined to have an acid slant and alkaline butt.  Our bacteria consumed the glucose, producing an acid as an end product to fermentation.  Once again, our bacteria didn't produce a gas as a by-product because there was no break in the agar.  This is a good result because it is consistent with the previous carbohydrate test. However these results are not typical.  There may have been some systematic error in our experiment.

Methyl Red/Voges-Proskauer Test:


After incubating our bacteria in a MR-VP broth for 48 hours, we separated its contents into two tubes.  To one, we added 5 drops of Methyl Red dye, and to the other, we added 15 drops of VP-A and 5 drops of VP-B.

The Results:
Methyl Red Test

After adding the drops, if our bacteria was positive for acid production, which it was, it would retain the red color of the dye.  However, if an acid was not the by-product of the experiment, the color would have faded to a distinct yellow.  Thus, our bacteria tested positive for acid fermentation.  A bacteria that commonly has an acid by-product is E. coli.  However, if you were following previous blogs, this could not be the case because our bacteria is a small cocci bacteria.  E. coli is bacilli.

Voges-Proskauer Test:

In a positive test, which this is not, there would be a reddish tint nearing the top of the tube.  Our bacteria did not show any change in color; therefore, it is negative for the fermentation of glucose via butanediol fermentation.  This means our bacteria does not degrade acids into non-acids.

Join us next week for more Microbiology Lab Adventures!  The Litmus Test will be ready!