Study of Staphylococcus aureus pathogenic genes by transfer and expressionin the less virulent organism Streptococcus goldonii

Because Staphylococcus aureus strains contain multiple virulence factors, s tudying their pathogenic role by single-gene inactivation generated equivoc al results. To circumvent this problem, we have expressed specific S. aureu s genes in the less virulent organism Streptococcus gordonii and tested the recombinants for a gain of function both in vitro and in vivo. Clumping fa ctor A (CIM) and coagulase were investigated. Both gene products were expre ssed functionally and with similar kinetics during growth by streptococci a nd staphylococci. ClfA-positive S. gordonii was more adherent to platelet-f ibrin clots mimicking cardiac vegetations in vitro and more infective in ra ts with experimental endocarditis (P < 0.05). Moreover, deleting clfA from clfA-positive streptococcal transformants restored both the low in vitro ad herence and the low in vivo infectivity of the parent. Coagulase-positive t ransformants, on the other hand, were neither more adherent nor more infect ive than the parent. Furthermore, coagulase did not increase the pathogenic ity of clfA-positive streptococci when both clfA and coa genes were simulta neously expressed in an artificial minioperon in streptococci, These result s definitively attribute a role for ClfA, but not coagulase, in S. aureus e ndovascular infections. This gain-of-function strategy might help solve the role of individual factors in the complex the S. aureus-host relationship.