Purpose: To study L. monocytogenes population changes and to determine the expression of its virulence-associated genes, after in vitro exposure to human gastric and duodenal aspirate.
Methods: Gastric and duodenal human fluids were collected endoscopically. L. monocytogenes cultures (16 h) of the strain LQC 15257 (serotype 4b) were inoculated in gastric fluid at 9 log CFU mL-1. Samples were incubated at 37oC for 100 min and then centrifuged. The precipitate was resuspended in duodenal fluid and samples were incubated at 37oC for 2 h. Population changes and gene expression were studied by culture-based methods and RT-qPCR, respectively.
Results: L. monocytogenes population was decreased in all studied cases; the microorganism was not detectable after its exposure to gastric aspirate in 11/12 patients with gastric pH<2.9 in contrast to 1/3 patients with gastric aspirate pH>2.9 (p=0.022). In 3/4 of gastric aspirates from patients who had previously received proton pump inhibitors (PPIs) the microorganism was also undetectable, versus 9/11 gastric aspirates from patients who had no previous PPIs intake (p=0.021). hly and inlC genes were over-expressed in 8/12 aspirates from patients with gastric pH<2.9 as compared to 1/3 with pH>2.9 and in 10/12 aspirates from patients with gastric pH<2.9 as compared to 1/3 pH>2.9, respectively. However, changes in the expression of prfA, sigB, plcA, plcB, InlA, InlB, InlJ, lmo2470 and lmo2672 genes were not associated with the pH of the gastric aspirate.
Significance: For the first time, a study simulated real exposure conditions using gastroduodenal human aspirates. Results indicated that conditions increasing gastric pH value, such as PPIs intake, may predispose patients to listeriosis.