The number of multiple antibiotic resistant bacteria is dramatically increasing and there is serious concern especially in hospitals. Bacterial species like Pseudomonas aeruginosa, Staphylococcus aureus or Achromobacter xylosoxidans play a role in different states of cystic fibrosis. This research project deals with the use of bacteriophages against these infectious bacteria as a promising alternative to antibiotics. Thereby two different research lines will be followed. The first line deals with the isolation and further characterisation of new bacteriophages in order to investigate their ability to lyse multiple resistant strains of Staphylococcus aureus and Achromobacter xylosoxidans for practical use. The second line analyses a possible role of these bacteriophages in evolution of both bacterial species as bacteriophages might act as vehicles for gene transfer by transduction.