Abstract
The colonization resistance conveyed by the intestinal microbiota can prevent colonization of the intestinal system by new strains. In this study, this resistance was partly circumvented by use of the antimicrobial drug norfloxacin. The colonization abilities of two closely related Escherichia coli strains, which were resistant to nalidixic acid and rifampin, respectively, were investigated in minipigs and a two-stage continuous-flow in vitro gut model. Whereas both strains were unable to colonize the intact enteric system in vivo and in vitro, a 3-day norfloxacin treatment modified both systems to allow colonization by the nalidixic acid-resistant strain but not the rifampin-resistant strain. The results indicate the usefulness of norfloxacin to circumvent the normal colonization resistance while keeping a fairly normal microbiota in the gut. The results also indicate that it could be possible to construct in vitro gut models which could distinguish between strains with different gut colonization abilities. Both of these possibilities could come to be used in the study of the colonization and effects in the gut of new bacterial strains, i.e., genetically modified microorganisms.