Growth advantage and enhanced toxicity of Escherichia coli adherent to tissue culture cells due to restricted diffusion of products secreted by the cells

This study was undertaken to examine whether Escherichia coli adherent to tissue cells gain advantages over nonadherent bacteria due to their proximity to the cells. We used tissue culture cells and isogenic derivatives of a proline auxotrophic strain of E. coli that were fimbriated (Fim⁺) or nonfimbriated (Fim^-), and were heat-labile enterotoxin producing (Tox⁺) or toxin nonproducing (Tox^-). We found that the Fim⁺ bacteria, which were capable of adhering to tissue culture cells, initiated growth much sooner than did nonadherent Fim^- bacteria; the adherent bacteria used tissue cell-derived proline, which was available at high concentrations only in the zone of bacterial adherence. Likewise, cyclic AMP secreted by adherent (Fim⁺) bacteria was maintained at high concentration on the tissue cell surfaces. As few as 2 x 10⁵ adherent Fim⁺ Tox⁺ bacteria exert toxic activity upon Y1 adrenal cells, whereas toxin secreted in the medium by 6 x 10⁶ Fim^- Tox⁺ bacteria was undetectable. The results suggest that the growth advantage and enhanced toxicity of adherent E. coli is due to restricted diffusion of products secreted by the tissue culture and bacterial cells, respectively.