  Let $\mathcal C$ be a class of topological semigroups. A semigroup $X$ is
$injectively$ $\mathcal C$-$closed$ if $X$ is closed in each topological
semigroup $Y\in\mathcal C$ containing $X$ as a subsemigroup. Let
$\mathsf{T_{\!2}S}$ (resp. $\mathsf{T_{\!z}S}$) be the class of Hausdorff (and
zero-dimensional) topological semigroups. We prove that a commutative semigroup
$X$ is injectively $\mathsf{T_{\!2}S}$-closed if and only if $X$ is injectively
$\mathsf{T_{\!z}S}$-closed if and only if $X$ is bounded, chain-finite,
group-finite, nonsingular and not Clifford-singular.
