Human Intestinal Cells Modulate Conjugational Transfer of Multidrug Resistance Plasmids between Clinical Escherichia coli Isolates.

Bacterial conjugation in the human gut microbiota is believed to play a major role in the dissemination of antibiotic resistance genes and virulence plasmids. However, the modulation of bacterial conjugation by the human host remains poorly understood and there is a need for controlled systems to study this process. We established an in vitro co-culture system to study the interaction between human intestinal cells and bacteria. We show that the conjugation efficiency of a plasmid encoding an extended spectrum beta-lactamase is reduced when clinical isolates of Escherichia coli are co-cultured with human intestinal cells. We show that filtered media from co-cultures contain a factor that reduces conjugation efficiency. Protease treatment of the filtered media eliminates this inhibition of conjugation. This data suggests that a peptide or protein based factor is secreted on the apical side of the intestinal cells exposed to bacteria leading to a two-fold reduction in conjugation efficiency. These results show that human gut epithelial cells can modulate bacterial conjugation and may have relevance to gene exchange in the gut

Colonization of the streptomycin-treated mouse large intestine by a human fecal Escherichia coli strain: role of adhesion to mucosal receptors.

Escherichia coli F-18, a normal fecal isolate, was previously shown to be an excellent colonizer of the streptomycin-treated CD-1 mouse large intestine, whereas E. coli F-18col-, a derivative of E. coli F-18 that no longer makes the E. coli F-18 colicin, was shown to be a poor mouse colonizer. It was also shown that E. coli F-18 bound two to three times more soluble colonic mucus protein than did E. coli F-18col- and that a major receptor in CD-1 mouse colonic mucus was a 50.5-kilodalton glycoprotein. In the present investigation, an additional E. coli F-18 colonic mucus glycoprotein receptor (66 kilodaltons) and three cecal mucus glycoprotein receptors (94, 73, and 66 kilodaltons) were identified. Numerous colonic and cecal brush border protein receptors specific for E. coli F-18 were also identified. Furthermore, E. coli F-18col- was found to bind to the same mucus and brush border receptors as E. coli F-18, although to a far lesser extent. Adhesion of both E. coli F-18 and F-18col- was inhibited by D-mannose and alpha-methyl-D-mannoside, and both strains were shown to bind specifically to the mannose moiety of a mannose-bovine serum albumin glycoconjugate, although again E. coli F-18col- bound to a lesser extent. Finally, both E. coli F-18 and F-18col- were shown to be piliated. The possible role of pilus mediated adhesion in E. coli F-18 colonization of the streptomycin-treated mouse large intestine is discussed

Role of catecholate siderophores in gram-negative bacterial colonization of the mouse gut

We investigated the importance of the production of catecholate siderophores, and the utilization of their iron (III) complexes, to colonization of the mouse intestinal tract by Escherichia coli. First, a ΔtonB strain was completely unable to colonize mice. Next, we compared wild type E. coli MG1655 to its derivatives carrying site-directed mutations of genes for enterobactin synthesis (ΔentA::Cm; strain CAT0), ferric catecholate transport (Δfiu, ΔfepA, Δcir, ΔfecA::Cm; CAT4), or both (Δfiu, ΔfepA, ΔfecA, Δcir, ΔentA::Cm; CAT40) during colonization of the mouse gut. Competitions between wild type and mutant strains over a 2-week period in vivo showed impairment of all the genetically engineered bacteria relative to MG1655. CAT0, CAT4 and CAT40 colonized mice 10[superscript 1]-, 10[superscript 5]-, and 10[superscript 2]-fold less efficiently, respectively, than MG1655. Unexpectedly, the additional inability of CAT40 to synthesize enterobactin resulted in a 1000-fold better colonization efficiency relative to CAT4. Analyses of gut mucus showed that CAT4 hyperexcreted enterobactin in vivo, effectively rendering the catecholate transport-deficient strain iron-starved. The results demonstrate that, contrary to prior reports, iron acquisition via catecholate siderophores plays a fundamental role in bacterial colonization of the murine intestinal tract