Surface-expressed Mig protein protects Streptococcus dysgalactiae against phagocytosis by bovine neutrophils

• Published in: Infection and immunity Vol. 69; no. 10; pp. 6030 - 6037
• Main Authors: SONG, Xin-Ming, PEREZ-CASAL, Jose, BOLTON, Alexandra, POTTER, Andrew A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.10.2001
• Subjects: a2-macroglobulin; alpha-Macroglobulins - immunology; alpha-Macroglobulins - metabolism; Animals; Bacterial Outer Membrane Proteins - genetics; Bacterial Outer Membrane Proteins - immunology; Bacteriology; Base Sequence; Biological and medical sciences; Cattle; Cell Membrane - metabolism; Cellular Microbiology: Pathogen-Host Cell Molecular Interactions; Cloning, Molecular; DNA, Bacterial; Escherichia coli; Fundamental and applied biological sciences. Psychology; Genes, Bacterial; Immunoglobulin G - genetics; Immunoglobulin G - immunology; Microbiology; mig gene; Mig protein; Molecular Sequence Data; Mutagenesis; Neutrophils - immunology; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Phagocytosis - immunology; Protozoa; Rabbits; Receptors, Cell Surface - genetics; Receptors, Cell Surface - immunology; Receptors, IgG - genetics; Receptors, IgG - immunology; Sequence Analysis, DNA; Streptococcus - genetics; Streptococcus - immunology; Streptococcus dysgalactiae; Vaccines, antisera, therapeutical immunoglobulins and monoclonal antibodies; Plasma; Escherichia coli; IgG; Binding protein; Pathogenic; Streptococcal infection; Streptococcus A; Bacteria; Micrococcales; Receptor protein; Ungulata; Enterobacteriaceae; Binding; Immunoglobulins; Mastitis; Bovine; Macroglobulins; Streptococcus dysgalactiae; Major gene; Infection; Mammary gland diseases; Streptococcaceae; Vertebrata; Mammalia; Bacteriosis; Isolate; Artiodactyla; Neutrophil; Phagocytosis
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.69.10.6030-6037.2001

The mig gene of Streptococcus dysgalactiae, a major bovine mastitis pathogen, encodes two plasma protein-binding receptors, alpha2-macroglobulin (alpha2-M) and immunoglobulin G (IgG). In this study, the mig gene from one S. dysgalactiae isolate was cloned and expressed in Escherichia coli. The IgG receptor region encoded by mig was conserved in 16 S. dysgalactiae strains. An isogenic mig mutant was constructed by allele replacement mutagenesis of the wild-type gene in S. dysgalactiae. The IgG-binding activity was lost in the mig mutant strain, whereas the alpha2-M receptor activity was still expressed but was detected only in the culture supernatant. In flow cytometry phagocytosis and bacterial-colony-counting bactericidal assays, the wild-type strain was found to be significantly more resistant to phagocytosis and killing by bovine neutrophils (PMNs) than the mig mutant strain when bacteria were preincubated with bovine serum. We therefore speculate that the Mig protein of S. dysgalactiae plays a role in virulence of the bacteria by binding to the plasma protein alpha2-M or IgG and thus preventing phagocytosis by bovine PMNs.