Discussion

Protocol Changes:     

            We decided to change our goal from isolating L. helveticus from Gruyere cheese to isolating it from spoiled milk. Gruyere cheese is a hard cheese that could not be plated directly onto the plates and spoiled milk was much simpler to streak on plates. The milk we were spoiling was placed in the incubator at 45șC to create optimum conditions for the growth of L. helveticus. We found through experimentation that dilutions were necessary in order to isolate individual colonies on TJA. A 10-2 dilution of the spoiled milk in sterile saline allowed us to isolate colonies. Initially, we allowed our plates to incubate for 48 hours.  However, by doing so, L helveticus overgrew, preventing isolated colonies from being obtained. After 48 hours, Gram stain results showed both gram positive and gram negative rods.  However, when the Gram stain was performed after 24 hours, the percentage of gram negative rods was greatly diminished.  We believe that L helveticus started to die off after 24 hours, causing inaccurate Gram stain results.  Therefore, we changed our protocol so that Gram stains were performed with cultures that had been incubated for only 24 hours.

  

Explanation of Results:

            The pure culture that we obtained has many characteristics of L. helveticus, leading us to conclude that we have successfully isolated L. helveticus. The results of the tests that we performed were consistent with our expectations of L. helveticus.  TJA has a relatively low pH, which selected against other bacteria in milk that might grow at higher pHs. Growing the bacteria at 45șC prevented the growth of Streptococci, which grows optimally at 37șC. L. helveticus is gram positive.  The Gram stain results of our isolate was also positive. The Gram stain revealed the presence of a rod and the absence of an endospore, two characteristics of L. helveticus.  The results from the sugar fermentation tubes were consistent with L. helveticus in that it fermented glucose and did not ferment mannitol and sucrose.  One result that was not consistent with our expectations for L. helveticus was the variable lactose fermentation.  Initially, we inoculated one lactose tube, read it after 24 hours, and observed a negative result when a positive result was expected. This could be attributed to the fact that the genus Lactobacillus is extremely sensitive to media composition and cultural conditions (Bergey’s). The test was repeated with two lactose tubes.  One tube displayed positive lactose fermentation, while the other illustrated negative lactose fermentation.  This variable fermentation of lactose could possibly have been caused by contamination or improper inoculation.  As expected, the catalase test was negative.

        

Practical Uses of Lactobacillus helveticus

            L. helveticus is used in the production of cheeses. The lactic acid it produces when it ferments gives Gruyere cheese its distinct flavor. Another interesting characteristic of Lactobacillus helveticus is its recently discovered ability to benefit human health. Recently, Lactobacillus helveticus has been used as a probiotic, a bacteria that is beneficial to human health. Lactobacillus has the ability to grow in the intestinal tract after ingestion. Fermented milk containing L. helveticus has been shown to lower blood pressure in people with hypertension. As L. helveticus ferments the milk, it makes proteolytic enzymes that cleave proteins to make ACE-inhibiting peptides that are believed to work similarly to ACE inhibitors currently used to lower high blood pressure. These drugs inhibit the production of the vasoconstrictor angiotensin and the degradation of the vasodilator bradykinin. In a recent study, the milk lowered both systolic and diastolic blood pressures over a period of 5 months (Seppo).                           

                                                                                                                                                           

The proteolytic activity of L. helveticus in fermented milks may also produce proteins that have immune enhancing and anti-tumor effects. In a study involving mice, those fed milk fermented with L. helveticus showed an increase in IgA-producing cells as well as a reduction in fibrosarcoma size (LeBlanc). Although still in early stages of research, consumption of L. helveticus seems to promise many benefits to human health.