Bacteria live all around us and in general they live peacefully in balance with us. Sometimes however this balance is disrupted when a bacteria starts to adapt and explore new areas. This is also the case for the gut bacterium Enterococcus faecium. Over the years it has acquired many antibiotic resistances and is causing, at an increasing rate, hospital associated infections. The goal of this research was to unravel which adaptions E. faecium has made that allowed it to become so successful as a hospital associated disease. For this we developed new genetic techniques to study its DNA and more easily manipulate the DNA to get a better understanding of the function of the genes. Our results show that not a singular gene responsible for the improved adaptation but a complex network of genes which are largely present across E. faecium strains. This indicates that this bacterium as a species is already highly suited to survive in hospitals. Further research needs to be conducted to understand in greater detail into how this bacterium survives and aim to discover new methods to prevent it from causing infections in hospitalised patients.