Abstract
Escherichia coli isolates from calves with diarrhea (1 day to 8 weeks old, 140 individuals) were surveyed for the three immunologically distinct fimbrial adhesins FY, 31A, and K99. Of a total of 1, 370 strains isolated, 96 (7.0%), 34 (2.5%), 75 (5.5%), and 13 (0.9%) were identified as FY+, 31A+, FY+•31A+, and K99+, respectively. The K99+ strains also manifested heat-stable enterotoxin production (ST+), while FY+, 31A+, and FY+•31A+ strains were ST-. Expression of FY and 31A was repressed at lower temperatures or poor aeration. The FY+ and 31A+ E. coli showed mannose-resistant hemagglutinating activity with bovine erythrocytes. Electron microscopy revealed that FY is a gently curled fimbria with a mean diameter of 4.2nm, and 31A is a fimbria with a mean diameter of 5.1nm. The molecular mass of protein subunits was found to be approximately 20 kilodaltons (Kd) and 19Kd for FY and 31A, respectively. Lethal diarrhea of neonatal calves was induced by challenge with the combination of a K99+•ST+ E. coli strain and either a 31A+ E. coli strain or a 31A+ E. coli strain plus an FY+ E. coli strain under the experimental conditions in which lethal diarrhea was not induced by challenge with a K99+•ST+ E. coli strain alone.
