The present invention relates to antibiotic-resistant bacteria, and to the prevention or treatment of infections of drug-resistant pathogens, such as carbapenem-resistant Enterobacteriaceae (CRE) and / or vancomycin-resistant Enterococcus (VRE). In particular, the invention relates to the treatment or prevention of colonisation of CRE and / or VRE in the gastrointestinal (GI) tract, before they cause invasive infections, for example in the blood. The invention provides novel formulations, pharmaceutical compositions and methods of using them to prevent or treat CRE and / or VRE infections or intestinal colonisations thereof.