  We show interior H\"older continuity for a class of quasi-linear degenerate
reaction-diffusion equations. The diffusion coefficient in the equation has a
porous medium type degeneracy and its primitive has a singularity. The reaction
term is locally bounded except in zero. The class of equations we analyse is
motivated by a model that describes the growth of biofilms. Our method is based
on the original proof of interior H\"older continuity for the porous medium
equation. We do not restrict ourselves to solutions that are limits in the weak
topology of a sequence of approximate continuous solutions of regularized
problems, which is a common assumption.
