SERUM RESISTANCE AND VIRULENCE OF ESCHERICHIA-COLI ISOLATED FROM TURKEYS

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Abstract
Twenty-five strains of Escherichia coli isolated from turkeys were characterized for their serum resistance and virulence. An in vitro bactericidal assay was used to determine the serum resistance of E. coli. Virulence was determined by survival time after i.v. inoculation of each strain into 3-week-old turkeys. Serum-resistant E. coli strains were generally found to be virulent for turkeys, whereas serum-sensitive E. coli strains were avirulent. Of the 25 strains, 18 strains were placed in the 2 categories of serum-resistant/virulent and serum-sensitive/avirulent. Five strains were serum-resistant and avirulent and 2 strains were serum-sensitive and virulent. Serum resistance appears to be an important determinant of virulence for E. coli in turkeys; however, the requirement for other virulence factors, in addition to serum resistance, was suggested by the finding that 5 serum-resistant strains were avirulent in turkeys.