Streptococcus uberis resists the bactericidal action of bovine neutrophils despite the presence of bound immunoglobulin.

Streptococcus uberis 0140J was more resistant to the bactericidal action of bovine neutrophils after growth in chemically defined medium (CDM) supplemented with casein hydrolysate than when grown in CDM alone. Neither adult bovine serum obtained prior to vaccination nor hyperimmune serum raised against this bacterium was capable of acting as an effective opsonin towards S. uberis grown in the presence of casein hydrolysate. There was no detectable difference in the ability of bacteria grown in either CDM or CDM supplemented with casein hydrolysate to bind immunoglobulin G1 (IgG1), IgG2, or IgM from either hyperimmune serum or preparations of immunoglobulin from the same serum. Bacteria of both the phagocytosis-resistant and phagocytosis-sensitive phenotypes presented the same amount of IgG2 Fc terminus on their surfaces. It is concluded that the inducible resistance of S. uberis to bactericidal action of bovine neutrophils is not mediated by inhibition of antibody binding.