Aspergillus fumigatus and Pseudomonas aeruginosa are the most prevalent fungal and bacterial pathogens associated with cystic fibrosis (CF)-related infections, respectively. Coinfection with both pathogens is associated with a deterioration in lung function. Despite the persistence of A. fumigatus in the CF airways from an early age, P. aeruginosa eventually predominates as the primary pathogen and chronic infection by these bacteria is associated with morbidity and mortality. P. aeruginosa has a profound capacity to adapt to the hostile conditions that characterize the CF airways. Nonetheless, several factors are likely to facilitate colonization in the airways, including a compromised host cellular response and alterations to the microbial environment, perhaps generated in part by other microorganisms, such as A. fumigatus. A. fumigatus is the causative agent of allergic bronchopulmonary aspergillosis (ABPA), a disease characterized by the induction of a hypersensitivity response in host cells. The interactions between A. fumigatus and host epithelial cells, such as the alveolar epithelial cell line A549, have been well characterized. The response of A549 cells to exposure by multiple pathogens is less well understood. With this in mind, a proteomic approach was employed to investigate changes to the proteome of A549 cells in response to exposure by A. fumigatus and P. aeruginosa. Label-free quantitative (LFQ) proteomics revealed distinct changes to the host-cell proteome in response to either or both pathogens. Alterations to the proteome were dependent on the duration and sequence of infection. The results presented in this thesis suggest that A. fumigatus render A549 cells unable to internalize bacteria, thus providing an environment in which P. aeruginosa can proliferate. Interaction studies between A. fumigatus and P. aeruginosa identified a key role for A. fumigatus in creating a nutrient-rich environment in which P. aeruginosa could proliferate. The emergence of antibiotic resistant bacteria, including P. aeruginosa has led to an urgency for the need to discover novel antibiotics. Saprophytic fungi inherently produce a range of antimicrobial compounds that enable competition in their ecological niche. Fortuitously for humans, these compounds can be exploited for medicinal purposes. The process of identification of one such potentially novel anti-bacterial compound produced by A. fumigatus is described here. The effect of the compound on the P. aeruginosa proteome was characterized by LFQ proteomics with a view to gaining insights into the mechanism of action by which the anti-bacterial agent inhibits bacterial growth. Taken together, the findings presented in this thesis offer novel insights into the complex dynamics that exist between the host, P. aeruginosa and A. fumigatus.