Purdue University Graduate School
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Comparison of Microbial Quality of Commercial Probiotic Dietary Supplements

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posted on 2019-10-16, 18:26 authored by Pin-Wen WangPin-Wen Wang
Probiotics provide positive health benefits and potentially can be used as a treatment and prevention for foodborne diseases. To provide such health effects, probiotic microbes must survive before and after consumption and successfully colonize the gastrointestinal tract in the human body and display antimicrobial properties. There is lacking of studies comparing survival and antimicrobial effects of probiotic bacteria in dietary supplements sold in USA. Therefore, 11 probiotic supplements were compared for their microbial quality. Viable counts of five supplements exceeded or closely met the counts listed on the label. Two supplements did not contain any live bacteria in one of the two tested lots and the remaining four had viable counts about 1-2 log lower than the claimed viable counts.

Nine products, containing viable counts in both tested lots, were further analyzed for their tolerance of simulated gastrointestinal (SGI) condition. The results show that the survival of probiotic bacteria in SGI condition depended on encapsulation and bacteria strains. Probiotic bacteria in the form of pearl exhibited better survival in simulated gastric juice than those in capsule form. Nine probiotic bacteria including seven Lactobacillus and two Bacillus coagulans were isolated from the nine products and identified. The nine isolates were resistance to 4 -7 out of eight tested antibiotics. Culture filtrates of the seven Lactobacillus isolates inhibited the growth of Escherichia coli O157:H7 and Salmonella Typhimurium but not Listeria monocytogenes. However, after adjusting pH to 6.5, none of the culture filtrates showed any growth inhibition effect. Five probiotic isolates, namely L. acidophilus La-5 and La-14, L. plantarum Lp-115 and 299v and L. rhamnosus GG, which had relatively higher viable counts after exposure to SGI were compared for their ability to adhere to HT-29 cells and to reduce adhesion of the three pathogens to HT-29 cells. After incubation for 1 h, L. plantarum Lp-115 displayed the highest mean adhesion ratio (25.9 ± 3.4 CFU/cell) whereas L. acidophilus La-5 and La-14 had the lowest two mean adhesion ratios which were 0.8±0.1 and 1.9±0.5 CFU/cell respectively. Adhesion reduction of the three pathogens on HT-29 cells varied depending on the probiotic strains, the pathogens, and the method for analysis (exclusion, competition, and displacement). Among the five, L. plantarum Lp-115 showed the strongest pathogen inhibition ability. It excluded >97% E. coli O157:H7 and >91% S. Typhimurium and displaced >96% L. monocytogenes on HT-29 cells. Lactobacillus plantarum v299G and L. rhamnosus GG also reduced adhesion of the three pathogens on HT-29 cells by the same mechanisms; however, the percentages of reduction were slightly lower. The L. acidophilus La-5 reduced > 93% E. coli O157:H7 on HT-29 cells by competition or displacement, and displaced about 94% L. monocytogenes on the cells. Nevertheless, it only reduced <28% S. Typhimurium on HT-29 cells by the three mechanisms. The L. acidophilus La-14 showed similar effects on adhesion reduction of the three pathogens on HT-29 cells. Overall, Nature’s way® Pearls was the best probiotic supplements since the form of pearl made the probiotic bacteria more resistant in SGI condition. Additionally, the L. plantarum Lp-115 in this supplement had the highest adhesion ratio and the best antimicrobial efficacy.


Degree Type

  • Master of Science


  • Biological Sciences

Campus location

  • Hammond

Advisor/Supervisor/Committee Chair

Wei-Tsyi Ting

Additional Committee Member 2

Feng-Song Wang

Additional Committee Member 3

Michael Zimmer

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