Assessing gastric viability of probiotics: real testing in real human gastric fluid

Abstract

Background: It is believed that the harsh conditions of the upper gastrointestinal tract, such as gastric fluid acidity, may affect the viability of ingested probiotics. Thus far, this notion has been verified in vitro by viability testing in simulated gastric fluid.
Objective: In this study, the survival of 8 probiotic bacteria was investigated in real human gastric fluid to determine the response of the bacteria in the actual biological medium.
Methods: Gastric tolerance of the different probiotic bacteria was determined by inoculation of the bacteria in human gastric fluid, sampling at 30 min, 60 min, 120 min, 180 min, serial dilution and spread plating. Tolerance was also determined in traditionally simulated fluids at pH of 2.2 ± 0.1 and 2.8 ± 0.1, mimicking the pH of the human gastric fluid.
Results: All the probiotic bacteria tested except for one strain, which showed less than 1 log CFU/mL loss in viability in the two fluids, were susceptible to the gastric fluids. The results showed significant (p < 0.05) strain-specific differences in the sensitivities of the bacteria in the gastric fluids. Some species were more sensitive to the real human gastric fluid than the simulated fluid. However, overall, the simulated gastric fluid did not significantly differ (p > 0.05) and hence provided a comparable environment to the actual human fluid at a similar pH.
Conclusion: More than 80% of the tested probiotic strains were susceptible to real human gastric fluids. The results demonstrated strain differences in the susceptibility of different probiotic bacteria to gastric fluid. Also noteworthy are the differences in the behaviour of some of the probiotic bacteria in the real fluid against the simulated fluid. The result highlights the importance of using biorelevant test systems in viability assays.