After originally swabbing the yogurt onto the LBS plates and incubating them, the growth on the plates showed two different colonies that looked the same except for the fact that they were different sizes. According to conducted research, Lactobacillus colonies are quite small. Therefore, it was apparent that the smaller colonies were indeed the colonies of interest. The lab tests were performed on bacteria that came from new plates streaked with only these colonies.
 

Interpretation of Results

All of the data that was collected enforces the fact that the bacterium isolated was indeed a Lactobacillus. Lactobacilli are rod shaped Gram positive bacteria. The test results from the Gram stain showed purple rods. This coincideswith the research because G+ bacteria stain purple. To double check stainingtechnique and to eliminate error, the bacteria were also plated on MacConkey'splates. MacConkey's media is a selective media that inhibits the growthof G+ bacteria. The fact that no growth resulted on those plates furtherconfirms the fact that the bacteria isolated were indeed G+. Another characteristicof Lactobacilli is the fact that they are unable to produce endospores. Many times endospores are seen in the Gram stain if they are present. Nonewere observed in the Gram stain but an endospore stain was done to doublecheck. No white or clear areas were visible within the green area of thestained cell; therefore no endospores were present. Because Lactobacilli are non-motile, it was necessary to inoculate a motility stab and observethe results. Bacteria that contain appendages that allow them to move ontheir own can migrate through the agar resulting in growth throughout theagar. Those bacteria that are not motile do not contain motor appendagesand growth is only along the stab line. Data shows that the bacteria testedwere non-motile, coinciding with Lactobacillus characteristics. Lactobacilli also lack the catalase enzyme that allows it to break downHydrogen Peroxide. The fact that no bubbles resulted in this test showedthat the isolated bacteria didn't contain the enzyme. Another importantcharacteristic of Lactobacilli is the fact that these types of bacteriacan grow with or without the presence of oxygen. Since the original batchwas incubated in an anaerobic chamber, it was obvious that the bacteria werecapable of growing in anaerobic conditions. But could they grow in the presenceof oxygen as Lactobacillus can? When incubated outside of the anaerobicchamber in the presence of oxygen the bacteria still grew. The isolatedbacteria, like Lactobacilli, were aerotolerant anaerobes. The lasttest was analyzed for various sugar fermentation. Both tests yielded positivecontrols (growth of the organism and a color change) indicating that theisolated bacteria, like Lactobacilli , could ferment both Glucose andLactose.

Every test that wasperformed yielded results that coincided with the characteristics of Lactobacilli. Furthermore the source (yogurt) is know for containing Lactobacilli . Therefore the isolated organism in the project was indeed a Lactobacillus.
 
 

Experimental Problems

In the beginning of the project, a major fact was overlooked. Because the yogurt container stated: "contains active cultures of L. Acidophilus ", it was prematurely assumed that Lactobacilli were the only type of bacteria that was present in the sample. This assumption, as was later discovered, was wrong! Numerous plates were streaked, but none were numbered. Various Gram stains were made from these plates but weren't numbered either so there was no way of tracing back to which slide coincided with which plate. Also, because it was assumed that only one type of bacteria (our targetbacteria) was present, careful technique wasn't practiced and more than onecolony at a time was picked off the plate and made into slides. When examiningthe stains, both pink and purple rods were present. Gram positive rods weresupposed to be isolated, not the pink negative ones. Testing couldn't proceeduntil a pure culture of these G+ rods was obtained. The yogurt had to bereswabbed onto more plates. This time they were numbered and only one colonyat a time was used for staining. After much time was wasted, a pure cultureof Lactobacillus resulted.
 
 

Ecological Significance of Lactobacillus

The most common application of Lactobacillus is industrial. These types of bacteria are extremely crucial to the food industry in particular. Because they produce acid as a byproduct of fermentation they help to preserve foods by making them acid and inhibiting the growth of other bacteria that can spoil the food. Lactobacilli are responsible for preserving food like cabbage to form sauerkraut, milk to form yogurt, and cucumbers to form pickles.

Lactobacillialso play a major role in the human health. This type of bacteria can befound in the vagina and the intestinal tract. In the vagina Lactobacilli inhibit the growth of yeast to prevent urogenital infections. They also prevent too much growth of E. Coli in the intestines to prevent gastrointestinal infections. Lately the pharmaceutical industry has taken advantage of these beneficial bacteria by incorporating it into dietary supplements, and advertising that the fact that Lactobacilli aren't harmful, but are even advantageous to human health.

The fact that Lactobacilli are so essential in the food industry is a major reason that this type of bacteria needs to be studied and isolated. Without it, millions of dollars would be lost in spoiled food and lack of profits from products such as yogurt. Furthermore the fact that Lactobacilli can be of some benefit tohuman health deserves further research.
 
 

For more information on the ecology of Lactobacillus,click here

For more information on the industrial significanceof Lactobacillus, click here