ABSTRACT
Objective To refine the infectious doses of enteric bacterial pathogens in animal assays and vaccine clinical trials by studying the invasion kinetics of five bacterial pathogens with human intestinal cells. Methods Utilizing in vitro cultured cell invasion assays with gentamicin-killing step, the invasive effects were analyzed in foodborne pathogens including Salmonella, Shigella, Yersinia, Escherichia coli (E. coli) O157 and opportunistic pathogens Citrobacter in human embryonic intestine 407 cells and ileocecum HCT-8 cells at multiplicities of infection (MOIs) of 0.04–4 000.00 E. coli HS served as a noninvasive control. Results The study results showed that the bacterial invasive efficiency and the average number of internalized bacteria per host cell changed with different starting MOIs. Higher starting MOIs did not always produce more bacterial internalization. The bacterial invasion effects varied with different bacterial strains and host cell lines. E. coli O157:H7 did invade human ileocecum HCT-8 cells. Conclusions This study shows that these bacteria possess different invasive patterns at various starting MOIs and also in different cell lines. The results could help to figure out the appropriate infectious doses of the bacteria in animal assays and in vaccine clinical trials. The bacterial invasion kinetics is also valuable in evaluating the safety and efficacy of live attenuated bacterial vaccines.