Mold issue in a leased house?

My roommates and i have recently signed a lease on a home. After about a week or so in the home a few of my roommates have developed what seem like mold-related symptoms. One roommate has a mold allergy and her reaction has been the most severe. Our landlord has been unhelpful in the situation and has denied the presence of mold in the house. We purchased a mold detecting kit and the petri dish has shown signs of mold growth within 24 hours, so we are convinced the house has mold. any advice on what to do would be greatly appreciated.