Are probiotics effective against E.coli?
Jerry Liu, Carlito Doebeli
Sir Winston Churchill Secondary
Floor Location : M 238 H

Although Escherichia coli is an important bacteria for maintaining digestive health, certain strains can be pathogenic, and have hospitalized many people throughout the years. The most commonly prescribed treatment for infections is antibiotics, which are given out so often that in about 50% of cases, antibiotics are not the optimal treatment for the infection. Because antibiotics are so widely used, many pathogenic bacteria are able to develop resistance to these antibiotics, and the bacteria will not respond to future antibiotic treatment when it is needed. These so-called superbugs are becoming an increasing global health threat and continued misuse of antibiotics could lead to further complications in the future.

This project explores the effects of the probiotic lactobacillus reuteri on the growth of E. coli laboratory strain BL-21 in the presence and absence of the antibiotic ampicillin. The results of the experiment were compared to control groups of E. coli; lactobacillus reuteri; and lactobacillus reuteri in the presence of ampicillin. We conducted these tests to gain a better understanding of the bacteria present in our digestive system and the effects that supplements of probiotics and antibiotics have on our digestive system.

Our hypothesis stated that if the probiotic lactobacillus reuteri and the antibiotic ampicillin are present in a population of E. coli, then the E. coli will grow less than in the presence of only probiotics or antibiotics, because the probiotics will compete with the antibiotic resistant E. coli for the nutrients in the agar.

To carry out our experiment, we made custom culture dishes containing nutrients and agar as well as different combinations of ampicillin and two concentrations of the probiotic mixed in with the LB agar solution, as well as E. coli. After we observed the growth of bacteria on the plates, we decided to perform gram stain on the samples to determine what kind of bacteria was growing on each plate. Through observations of bacterial growth on the culture dishes, we determined that the probiotics were not effective in inhibiting the growth of E. coli on their own, and that the probiotics did not grow significantly in the presence of E. coli at all. The results also showed that the probiotics developed resistance to antibiotics, while the few E. coli that did grew in filamentous form. While the results of the experiment did not prove our hypothesis to be true, they showed a lot about the effects of probiotics and antibiotics on bacterial growth. It is important to continue to be aware of issues concerning bacteria, antibiotics, and personal digestive health in order to be safer in the future.