Polymicrobial infections involving fungi and bacteria are extremely difficult to treat due to the different species present and the ability of the microorganisms to produce a biofilm. Relatively little is known about the mechanisms that regulate the interspecies interactions that occur during fungal/bacterial infections. The majority of research to date has focused on the interactions between Candida albicans and bacteria, such as Staphylococcus aureus. However, non-albicans Candida such as Candida parapsilosis are emerging as significant fungal pathogens. There are no studies describing the interactions that occur between C. parapsilosis and S. aureus. Preliminary data indicates that C. parapsilosis inhibits S. aureus biofilm formation. This suggests an antagonistic relationship exists between these two important pathogens and could explain why they are rarely co-isolated from the same polymicrobial infection. This antagonistic relationship is in contrast to the synergism observed between C. albicans and S. aureus. This will be the first study to investigate the interactions between C. parapsilosis and S. aureus. They key goals are to characterize the C. parapsilosis/S. aureus inter-species interactions, to identify the key regulators of the interactions and to determine the transcriptional changes that occur during co-infection.