Transit tolerance in the simulated upper human gastrointestinal (GI) tract was assessed using an
in vitro model by adding gastric and pancreatic juices, as reported by
Charteris et al.(1998), with slight modifications. Simulated gastric juice (SGJ)
was prepared by dissolving pepsin from porcine gastric mucosa
in 0.5% w/v sterile saline to a
final concentration of 2 g/l and adjusting the pH to 2.5. Simulated small intestinal juice (SSIJ)was prepared by dissolving pancreatin from porcine pancreas,
250 mg/l, and porcine bile extract, 0.45%, in 0.5% w/v sterile
saline and adjusting the pH to 7.5. All chemicals were obtained
from Sigma Aldrich (St. Louis, MO). The solutions were prepared
fresh the same day as the experiment. Bacterial tolerance to SGJ
and to SSIJ were tested by mixing 15ml of bacterial suspension with 1000ml of gastric or small intestinal juice and 485m lof0.5%w/v sterile saline, obtaining a bacterial cell density around 109 cfu/ml. The average final pH of the simulated mixtures was 2.62 and 7.46 for the pH 2.5 and pH 7.5 for SGJ and for SSIJ,
respectively. The mixture was vortexed at maximum settings for
10 s and incubated at 37C. For testing gastric tolerance, 100ml was removed after 90 and after 120 min for determination of viable counts. Tolerance to SSIJ was determined by removing 100ml after 120 and after 240 min. To determine the number of
viable counts, serial dilutions were placed on MRS agar and
aerobically incubated at 30 or 37C for 48 h before enumeration
of colony forming units. The number of colony forming units was
expressed as log values, and tolerance over time was compared
for the investigated strains.