Food Science and Technology Department


Date of this Version



Cano Roca, C. 2014. Characterization of Commercial Probiotics: Antibiotic Resistance, Acid and Bile Resistance, and Prebiotic Utilization. Master's Thesis, University of Nebraska


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Food Science and Technology, Under the Supervision of Professor Jayne Stratton. Lincoln, Nebraska: August, 2014

Copyright (c) 2014 Carmen Lucia Cano Roca.


Probiotics, live microorganisms that beneficially affect the health of their host, must undergo extensive research to ensure they are safe for consumption and possess certain functional properties. Antibiotic resistance in probiotics has raised concern due to the possibility of its transfer to pathogens. Acid and bile tolerance ensures that organisms will survive passage into the intestines. Prebiotic utilization indicates ability to ferment specific carbohydrates for enhanced growth. The objective of this study was to characterize a group of commercial probiotics for their suitability as probiotics.

Nine commercial probiotic strains (7 Lactobacillus, 1 Lactococcus lactis, and 1 Bifidobacterium longum) were evaluated. Two methods, disk diffusion and broth microdilution, were utilized to determine susceptibility to 9 antibiotics (ampicillin, chloramphenicol, clindamycin, erythromycin, gentamycin, kanamycin, oxytetracycline, streptomycin, and vancomycin). Most strains were susceptible to 4 or more antibiotics. Only one strain, Lactobacillus salivarius, showed resistance to three antibiotics. The two methods tested were in agreement for 76.8% (63/82) of the bacteria-antibiotic combinations tested.

The cultures were assessed for their ability to utilize four prebiotics: galactooligosaccharides (GOS), two fructooligosaccharide (FOS), and inulin. Glucose was used as a positive control for growth. Galactooligosaccharides were fermented by seven strains and fructooligosaccharides derived from chicory, by two strains. Inulin did not promote significant growth of any of the strains.

Additionally, Bacillus coagulans ProDura is a sporeforming bacterium that has recently been identified and marketed as a novel probiotic with a greater ability to survive the low pH of the stomach when in spore form. This organism showed high tolerance to acid and bile conditions, with only a two log reduction after four hours at pH 2.0, and only a one log reduction in bile salts. It was susceptible to all antibiotics tested and was able to utilize GOS and FOS, but not inulin. In conclusion, the strains evaluated comply with the functional and safety characteristics of probiotics, except for the strain of Lactobacillus salivarius which demonstrated an unacceptable level of antibiotic resistance.

Adviser: Jayne Stratton