Human monoclonal antibodies against Staphylococcus aureus surface antigens recognize in vitro and in vivo biofilm

Implant-associated Staphylococcus aureus infections are difficult to treat because of biofilm formation. Bacteria in a biofilm are often insensitive to antibiotics and host immunity. Monoclonal antibodies (mAbs) could provide an alternative approach to improve the diagnosis and potential treatment of biofilm-related infections. Here, we show that mAbs targeting common surface components of S. aureus can recognize clinically relevant biofilm types. The mAbs were also shown to bind a collection of clinical isolates derived from different biofilm-associated infections (endocarditis, prosthetic joint, catheter). We identify two groups of antibodies: one group that uniquely binds S. aureus in biofilm state and one that recognizes S. aureus in both biofilm and planktonic state. Furthermore, we show that a mAb recognizing wall teichoic acid (clone 4497) specifically localizes to a subcutaneously implanted pre-colonized catheter in mice. In conclusion, we demonstrate the capacity of several human mAbs to detect S. aureus biofilms in vitro and in vivo.

Kinetic and structural characterization of spinach carbonic anhydrase

We have carried out kinetics studies of spinach carbonic anhydrase (CA) using stopped-flow spectrophotometry at steady state and 13C-NMR exchange at chemical equilibrium. We found that the rate of CO2<-->HCO3- exchange catalyzed by spinach CA at pH 7.0 to be 3-5 times faster than the maximal kcat for either CO2 hydration or HCO3- dehydration at steady state, suggesting a rate-determining H+ transfer step in the catalytic mechanism. Correspondingly, we measured a pH-independent solvent deuterium isotope effect on kcat of approximately 2.0, and found that the rate of catalysis was significantly decreased at external buffer concentrations below 5 mM. Our results are consistent with a zinc-hydroxide mechanism of action with for spinach CA, similar to that of animal carbonic anhydrases. We have also collected X-ray absorption spectra of spinach CA. Analysis of the extended fine structure (EXAFS) suggests that the coordination sphere of Zn in spinach CA must have one or more sulfur ligands, in contrast to animal CAs which have only nitrogen and oxygen ligands. The models which best fit the data have average Zn-N(O) distances of 1.99-2.06 A, average Zn-S distances of 2.31--2.32 A, and a total coordination number of 4-6. We conclude that animal and spinach CAs are convergently evolved enzymes which are structurally quite different, but functionally equivalent.