Serum susceptibility of coliforms isolated from bovine intramammary infections

A total of 35 coliforms isolated from bovine intramammary infections were tested for serum susceptibility. Growth responses of Klebsiella pneumoniae isolated from intramammary infections originating during the dry period were inhibited more than were growth responses of Klebsiella pneumoniae isolated from infections originating during lactation. Escherichia coli growth responses did not differ between isolates originating from dry period and lactational intramammary infections. Mean growth responses to serum did not differ between Klebsiella pneumoniae and Escherichia coli. Bactericidal properties of serum were due to complement activity. The classical pathway of complement appeared to be the principal source of bactericidal activity of serum toward Klebsiella pneumoniae. Alternative and classical pathways of complement were both important for bactericidal effects of serum on Escherichia coli. Iron saturation of serum did not affect growth responses of either Klebsiella pneumoniae or Escherichia coli. These data illustrate that coliforms isolated from intramammary infection originating during the dry period were not more resistant to the bactericidal activity of bovine serum than were coliforms isolated from intramammary infection occurring during lactation.