The infection of a mammalian host by a microorganism can be prevented or treated through the alteration of the C. albicans homologue of the high affinity phosphodiesterase, PDE2, gene and/or the adenylate cyclase-associated protein gene. These methods may be used in the identification, prevention or treatment of microbial infection of mammalian hosts such as immunocompromised or immunosuppressed humans, for example, those having AIDS or undergoing transplantation or anti-cancer therapy.