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Human lactoferrin binding in clinical isolates of Staphylococcus aureus
A S Naidu1, J Miedzobrodzki, J M Musser
1Department of Medical Microbiology, University of Lund, Malmö General Hospital, Sweden.
Abstract:
Human lactoferrin (HLf) is an iron-binding protein and a host-defence component at the mucosal surface. Recently, a specific receptor for HLf has been identified on a strain of Staphylococcus aureus associated with toxic shock syndrome. We have looked for the occurrence of 125I-HLf binding among 489 strains of S. aureus isolated from various clinical sources. HLf binding was common among S. aureus strains associated with furunculosis (94.3%), toxic shock syndrome (94.3%), endocarditis (83.3%) and septicaemia (82.8%) and other (nasal, vaginal or ocular) infections (96.1%) with a mean binding (in fmol) of 29.1, 21.9, 16.9, 22.2 and 29.2 respectively; the differences between mean HLf binding values of 29.1-29.2, 21.9-22.2 and 16.9 were significant. Furunculosis-associated (low-invasive or localised) isolates were high-to-moderate binders of HLf; 50% gave positive results at a threshold of greater than 31 fmol of 125I-HLf bound. In contrast, endocarditis-associated (high-invasive or systemic) isolates demonstrated low binding and did not bind 125I-HLf at the above threshold level. S. aureus recognised human or bovine Lf. However, bound 125I-HLf was more effectively inhibited in a dose-dependent manner by unlabelled bovine Lf than by homologous HLf. Binding of 125I-HLf to staphylococci was optimal with organisms grown in agar compared with those from broth cultures. The binding capacity of S. aureus was abolished when strains were grown on carbohydrate- and salt-rich agar media. HLf-binding ability of S. aureus did not correlate with fibronectin, fibrinogen, immunoglobulin G or laminin binding.
Insights
Human lactoferrin (HLf) binds to Staphylococcus aureus, a common bacterium. Binding levels varied with infection type, with lower binding seen in invasive diseases like endocarditis.
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.