P-039. Escherichia coli O157:H7 Strains that Persist in Cattle Populations Are Characterized by Enhanced Ability to Adhere to Human Intestinal Epithelial Cells

B. A. Carlson, J. N. Sofos, G. C. Smith, K. E. Belk, K. K. Nightingale;
Colorado State Univ., Fort Collins, CO.

Infection by Escherichia coli O157:H7, an enteric pathogen that attaches to the host’s intestinal epithelium, can cause human hemorrhagic colitis and hemolytic uremic syndrome possibly resulting in death. Escherichia coli O157 isolates from cattle fecal samples collected over six samplings during the final 120 d of the finishing period were characterized by (i) multiplex PCR to detect E. coli O157:H7 specific sequences (rfbE and fliCH7) along with virulence factors (eaeA, stxI and stxII) and (ii) pulsed field gel electrophoresis (PFGE). The pathogenic potential of E. coli O157 isolates representing different multiplex PCR genotypes was assessed by their ability to adhere to the Caco-2 human intestinal epithelial cells. E. coli O157:H7 isolates lacking both stxI and stxII or just stxI showed a greater (P < 0.05) ability to attach to Caco-2 cells as compared to all other genotypes, suggesting that attachment efficiency in human intestinal cells is shiga toxin independent. PFGE typing of isolates that carried all five multiplex PCR genes revealed a dominant subtype that accounted for more than 50% of all isolates characterized. This dominant PFGE subtype persisted within the animal population as indicated by a frequency of isolation for this subtype ranging from 32-88% during the six collections performed over 120 d. E. coli O157:H7 isolates belonging to the dominant PFGE subtype demonstrated significantly greater attachment efficiency to Caco-2 cells (P < 0.001) compared to isolates differing by 3 or more bands. There was a clear correlation (P < 0.001) between genetic divergence from the dominant subtype and decreased attachment efficacy, where isolates differing by 7 bands from the dominant subtype showed the lowest attachment efficiency. Our data show that certain E. coli O157:H7 strains may persist in cattle populations, which may be explained by an enhanced ability to adhere to the intestinal epithelium. Strains that persist in cattle populations are more likely to be transmitted to humans and may demonstrate greater pathogenic potential in humans, due to enhanced ability of these strains to attach to human intestinal epithelial cells.