Type III group B streptococcal strain differences in susceptibility to opsonization with human serum

Area of Science:

• Immunology
• Microbiology
• Vaccinology

Background:

• Group B Streptococcus (GBS) is a significant pathogen.
• Human serum opsonins are crucial for combating GBS infections.
• Variability in GBS strain susceptibility to opsonization exists.

Purpose of the Study:

• To investigate human serum opsonin activity against type III GBS strains.
• To evaluate the efficacy of pneumococcal vaccine immunization in inducing opsonic antibodies to GBS.
• To identify bacterial factors contributing to GBS resistance to phagocytosis.

Main Methods:

• In vitro opsonophagocytic assay using human sera and type III GBS strains.
• Immunization of individuals with pneumococcal vaccine.
• Neuramindase treatment of GBS strains followed by fluorescent lectin-binding assay.
• Antibody absorption assays.

Main Results:

• Significant variability in serum opsonic titers against different type III GBS strains.
• Pneumococcal vaccine immunization primarily increased opsonic titers against susceptible GBS strains, not resistant ones.
• Neuramindase treatment rendered resistant GBS strains susceptible to neutrophil killing, suggesting sialic acid as an antiphagocytic factor.
• Both susceptible and resistant GBS strains absorbed opsonic antibodies, indicating antibody binding is not sufficient for phagocytosis.

Conclusions:

• Opsonic activity against one GBS strain does not predict activity against others.
• Core antigen immunization is insufficient to induce protective opsonic antibodies against all GBS strains.
• Functional antibody assays are essential, as antibody binding does not always correlate with bacterial killing.