Human lactoferrin binding in clinical isolates of Staphylococcus aureus

* Department of Medical Microbiology, University of Lund, MalmÖ General Hospital, S-214 01 MalmÖ, Sweden, Staphylococcus Laboratory, Statens Seruminstitut, Amager Boulevard 80, DK2300 Copenhagen S., Denmark Department of Pathology and Laboratory Medicine, William Pepper Laboratory, Hospital of the University of Pennsylvania, Philadelphia, PA 19104--4283, USA, Staphylococcus Laboratory, Statens Seruminstitut, Amager Boulevard 80, DK2300 Copenhagen S., Denmark Department of Infectious Diseases, Halmstad Hospital, S-301 85 Halmstad, Sweden Received August 21, 1990 Accepted October 8, 1990 Summary. 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 125 I-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>>31 fmol of 125 I-HLf bound. In contrast, endocarditis-associated (high-invasive or systemic) isolates demonstrated low binding and did not bind 125 I-HLf at the above threshold level. S. aureus recognised human or bovine Lf. However, bound 125 I-HLf was more effectively inhibited in a dose-dependent manner by unlabelled bovine Lf than by homologous HLf. Binding of 125 I-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.