Mould in bathrooms exists because condensation/water collects and lingers. You will largely stop it by letting the room ventilate after using the bath or shower or cleaning up any residual water as soon as possible with a towel.
Improperly shaped bathroom sealant doesn't help as some of them collect reservoirs of water which sits and becomes home to mould also.
I don't think it is particularly unhygienic, certainly nothing the average student shouldn't be able to shake off. I would clean it up if I knew my new girlfriend was coming around mind...