EFFECT OF HYPOXIA ON ENTEROCYTE ENDOCYTOSIS OF ENTERIC BACTERIA

Objective: To clarify the effect of hypoxia on bacteria-enterocyte int eractions. Design: Randomized. Setting: Research laboratory. Subjects: Enteric bacteria and cultured human intestinal epi thelial cells, HT- 29 cells, Interventions: The effect of hypoxia on bacterial internaliz ation and intracellular survival was studied, using enterocytes cultur ed for 21 days in either 20%, 10%, or 5% oxygen, The effect of bacteri al growth conditions on bacterial internalization by enterocytes was s tudied, using bacterial cells in either the log phase or stationary ph ase of aerobic growth, and using bacterial cells in stationary phase, grown either under low oxygen conditions or under anaerobic conditions . Measurements and Main Results: Individual strains of enteric bacteri a were incubated with HT-29 cells for 1 hr. Numbers of internalized ba cteria were subsequently quantified after enterocyte lysis, Bacterial growth conditions (anaerobic vs, aerobic and log-phase vs. stationary- phase bacterial cells) had no noticeable effect on the numbers of Salm onella typhimurium, Proteus mirabilis, and Escherichia coli internaliz ed by enterocytes, Enterocytes cultivated in 20%, 10%, or 5% oxygen we re >95% viable, Enterocytes cultivated in 20% oxygen were confluent, b ut those enterocytes cultivated in hypoxia were not confluent and were fewer in number compared with enterocytes cultivated in normoxia. Com pared with enterocytes grown in normoxia, enterocytes cultivated in 5% and 10% oxygen internalized greater numbers of each of seven strains of enteric bacteria, including Listeria monocytogenes (two strains), E nterococcos faecalis (two strains), and P. mirabilis, E. coli (two str ains), with statistically significant increases noted for five of thes e seven bacterial strains. Intracellular survival of L. monocytogenes and P. mirabilis was assayed, Both species survived intracellularly fo r 22 hrs, with no noticeable differences in the numbers of intracellul ar bacteria recovered from enterocytes cultivated in 20%, 10%, and 5% oxygen, Conclusion: These in vitro results suggest that augmented bact erial endocytosis by enterocytes might at least partially explain the increased frequency of bacterial translocation associated with tissue ischemia.