  We consider the construction of integrable quantum field theories in the
operator-algebraic approach, which is based on quantum fields localized in
infinitely extended wedge regions. This approach has been successful for the
construction of a class of models with scalar $S$-matrices and without bound
states. In extension of these results, we apply similar methods to $S$-matrices
with poles in the physical strip (``bound states''). Specifically, we consider
a deformed version of the Sine-Gordon model, containing only breathers. We
exhibit wedge-local fields in this model, which differ from those in non-bound
state models by an additive term, the so called ``bound state operator''.
