Bactericidal and opsonic activities of normal sheep serum against gram-negative bacteria.

The bactericidal and opsonic activities of normal sheep serum against 9 smooth and 4 rough strains of gram-negative bacteria were measured. Three smooth strains-Escherichia coli 3662, Salmonella typhimurium, and Salmonella gallinarum-were resistant to the bactericidal action of normal sheep serum with or without complement. Six smooth strains-E coli O78:K80(B), Salmonella arizonae, Proteus inconstans, Klebsiella pneumoniae, Salmonella stanley, and Salmonella abortus-equi-were moderately sensitive to bactericidal activity of fresh sheep serum. After complement was added, serum heated at 56 C for 30 minutes did not regain its bactericidal activity against E coli O78:K80(B), P inconstans, nor S abortus-equi. Four rough strains-E coli Lilly, Salmonella cholerae-suis, Shigella sonnei, and Hafnia alvei-were very sensitive to the bactericidal activity of normal sheep serum. Somatic agglutinins were demonstrated in all of the sheep serums against all of the bacteria, but this antibody activity was partially destroyed by heating at 56 C for 30 minutes. The opsonic activity of normal sheep serum was demonstrated in normal mice. In the mouse peritoneal cavity, normal sheep serum enhanced opsonic activity against all smooth strains and 1 rough strain of the bacteria. The other 3 rough strains were extremely sensitive to the opsonic system of normal mice.