Identification of lactoferrin-binding proteins in bovine mastitis-causing Streptococcus uberis

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Protein-Ligand Interactions

Background:

• Streptococcus uberis is a significant mastitis pathogen.
• Lactoferrin (Lf) is an iron-binding milk protein with antimicrobial properties.
• Bacterial iron acquisition is crucial for pathogenesis.

Purpose of the Study:

• To investigate the interaction between Streptococcus uberis and lactoferrin (Lf).
• To identify bacterial components involved in Lf binding.
• To understand the potential role of Lf binding in bacterial iron acquisition.

Main Methods:

• Polyacrylamide gel electrophoresis and Western blotting to detect bacterial binding to Lf.
• Biotin-avidin-based microplate binding assay and ELISA to quantify bacterial binding to purified Lf.
• Inhibition assays using mannose, galactose, and bovine transferrin to probe binding specificity.

Main Results:

• All tested Streptococcus uberis strains bound to Lf in milk.
• Bacterial binding to Lf was confirmed using multiple assay methods.
• Binding was not inhibited by mannose or galactose, suggesting non-glycosidic interactions.
• Bovine transferrin did not affect Lf binding.
• Western blot analysis identified at least two bacterial proteins mediating Lf binding.

Conclusions:

• Streptococcus uberis possesses surface proteins that bind to milk lactoferrin.
• The binding mechanism does not involve the glycosidic domains of Lf.
• Lf binding represents a potential mechanism for Streptococcus uberis to acquire iron, supporting its growth and survival in the host.