Remedy against mould in the bathroom

We don't have much ventilation in our bathroom, and although I make sure to open the window and keep it open for some time, we keep having the odd black streaks appearing in the grouting and the silicon around the windows. Anything we can do about that?

Dry things with an e-cloth after use, if you can: mould grows in damp places. It will be condensation round the windows, so try to keep an eye on that. Otherwise, clean regularly with white vinegar - just a spritz of it diluted in water in a spray bottle.
It may not be possible to eliminate it entirely: it gets under the surface of the grout, and once it's there, it will leave a mark.

Thanks bertiebear, I'm already trying to dry all around the bathtub, didn't think about the window - and you're right, it gets into the silicone/grouting/window putty