Scientists have developed a new method to genetically engineer bacteriophages—viruses that infect bacteria—to fight antibiotic-resistant Staphylococcus aureus infections. Using CRISPR technology, they created a special phage that glows when it infects S. aureus cells, allowing doctors to quickly detect this dangerous pathogen in patient blood samples and other clinical samples. This engineered phage works against most S. aureus strains tested, regardless of their resistance to vancomycin, and could lead to new diagnostic tools and treatments for drug-resistant bacterial infections.