Streptococcus A question

[biology_06er]

Hi there,

I'm currently reading about adhesins in GAS and have a question regarding this statement (and sorry if it sounds dumb but I don't understand):

An additional FnBP, SfbX is encoded by a gene immediately downstream of sof. The two genes were found expressed in the same transcription unit and sfbX was present only in sof positive isolates. Recombinant SfbX bound to immobolized Fn and partially inhibited S. pyogenes adherence to Fn.

What I don't get is the part in bold writing...if s. pyogenes contains SfbX it would bind to Fn right..as it happens during infection/adherence in general...but I assume the recombinant SfbX is competing with s. pyogenes in this instance to bind to Fn..so my question is why does the recombin bind and not the s.pyogenes

hope i am making sense
thx guys
b_06er

[JackBean]

If I understand the experiment correctly, they had immobilized Fn, added recombinant SfbX, washed and added the bacteria.
Thus, first the recombinant protein bound to the immobilized one and thus it looked, like if there was less of the protein and the bacteria could not bind so well.