Human lactoferrin binding in clinical isolates of Staphylococcus aureus

Area of Science:

• Microbiology
• Immunology
• Biochemistry

Background:

• Human lactoferrin (HLf) is an iron-binding protein crucial for mucosal defense.
• A specific receptor for HLf has been identified on Staphylococcus aureus strains.
• Staphylococcus aureus is a significant human pathogen responsible for various infections.

Purpose of the Study:

• To investigate the prevalence and characteristics of HLf binding among diverse Staphylococcus aureus clinical isolates.
• To determine if HLf binding correlates with specific S. aureus infection types or invasiveness.
• To explore factors influencing HLf binding, including the source of lactoferrin and bacterial growth conditions.

Main Methods:

• Radiolabeled 125I-HLf binding assays were performed on 489 Staphylococcus aureus strains from various clinical sources.
• HLf binding was quantified and compared across isolates associated with different infections (furunculosis, toxic shock syndrome, endocarditis, septicaemia).
• Inhibition assays using unlabeled bovine lactoferrin and studies on bacterial growth media were conducted to understand binding specificity and conditions.

Main Results:

• HLf binding was prevalent across S. aureus isolates, with high rates observed in furunculosis, toxic shock syndrome, and other infections.
• Lower HLf binding was significantly associated with invasive infections like endocarditis.
• Bovine lactoferrin showed more effective inhibition of HLf binding than homologous HLf, and binding was optimal on agar cultures, abolished by carbohydrate/salt-rich media.

Conclusions:

• HLf binding is a common trait in Staphylococcus aureus, but its level varies with infection type and invasiveness.
• The findings suggest a potential role for HLf-S. aureus interactions in disease pathogenesis.
• Bovine lactoferrin may serve as a useful tool for studying HLf-receptor interactions, and growth conditions significantly impact binding capacity.