Modulating the microbial colonization of the gastrointestinal tract by oral administration of defined Escherichia coli strains. I. Influencing the biotope by means of metabolic drift mutants of Escherichia coli.

Through the selection of spontaneous metabolic drift mutants (selection marker RifR) of an Escherichia coli strain (O6:H2 SmR) of known settling capacity in conventional mice, it was attempted to obtain clones with positively optimized in vitro characteristics, which may exert a promotive influence upon the in vivo colonizing behaviour. Using 512 drift mutant strains (E. coli O6:H2 SmR RifR) we were able to establish positive optimizations, at an over-aleatory rate, for each of the in vitro characters tested (haemagglutination capacity of rabbit, guinea pig, and fowl erythrocytes; overgrowing power of mouse-adapted wild-type E. coli strains; formation of biomass with exclusive utilization of dextrose, lactose, fructose, adonitol, salicin, rhamnose, mannose; multiplying power; quantitative motility; and capacity to synthesize mucus). A higher settling rate (larger number of animals in which the test strain shared greater than or equal to 50% of the Enterobacteriaceae population than that obtained with the initial strain) could be established for one out of the 62 clones tested in vivo (a rise from 20% to 55%). The higher settling rate was associated with combinations of various functional parameters and not with an improvement of any of the individual functions. Despite the increase in settling rate relative to the number of experimental animals used in these studies, it was not generally possible to obtain a more than 3 days' dominance of the test strain within the lac+ Enterobacteriaceae. This is considered to be due primarily to the incipient synthesis of secretory IgA.