Staphylococcus aureus fibronectin binding proteins are essential for internalization by osteoblasts but do not account for differences in intracellular levels of bacteria

Staphylococcus aureus is a major pathogen of bone that has been shown to be internalized by osteoblasts via a receptor-mediated pathway. Here we repor t that there are strain-dependent differences in the uptake of S. aureus by osteoblasts. An S, aureus septic arthritis isolate, LS-l, was internalized some IO-fold more than the laboratory strain 8325-4. Disruption of the gen es for the fibronectin binding proteins in these two strains of S, aureus b locked their ability to be internalized by osteoblasts, thereby demonstrati ng the essentiality of these genes in this process. However, there were no differences in the capacity of these two strains to bind to fibronectin or osteoblasts, Analysis of the kinetics of internalization of the two strains by: osteoblasts revealed that strain 8325-4 was internalized only over a s hort period of time (2 h) and to low numbers, while LS-1 was taken up by os teoblasts in large numbers for over 3 h, These differences in the kinetics of uptake explain the fact that the two strains of S, aureus are internaliz ed by osteoblasts to different extents and suggest that in addition to the fibronectin binding proteins there are other, as Set undetermined virulence factors that play a role in the internalization process.