A team of researchers from the University of Colorado Anschutz School of Medicine is building a library of bacteriophages—viruses that specifically infect bacteria—to combat antibiotic-resistant infections. These phages have been studied for decades but are now receiving new attention as drug-resistant bacteria become a growing public health concern. The researchers are particularly interested in bacteria like Enterococcus faecalis and Enterococcus faecium, which are known for their resistance to many antibiotics and can cause serious infections in people with weakened immune systems. Other bacteria under study include Enterobacter hormaechei and Klebsiella oxytoca, both of which are also challenging to treat with conventional drugs. Bacteriophages function by attaching to bacterial cells and injecting their genetic material, which can disrupt the bacteria's ability to survive or replicate. Unlike human-infecting viruses, phages cannot harm human cells, but they can cause similar damage within bacterial cells. To find new phages, the researchers collect untreated wastewater, which contains a diverse range of bacteria found in the human gut. After exposing these bacteria to the wastewater, the team grows them on agar plates, where phages can be identified by the clear, round areas they create in the bacterial colonies. These phages are then isolated using a centrifuge, purified, and stored in special solutions that keep them stable for long periods. The research team has already identified over 30 different phages that can infect Enterococcus bacteria and between 15 to 20 that target Enterobacter and Klebsiella species. Some of these phages can infect multiple strains of a particular bacteria, while others are highly specific to a single strain, making them a very precise tool for targeting infections. Phages have shown potential as a treatment option, especially when used alongside traditional antibiotics. They can be administered orally, intravenously, or applied directly to wounds, offering flexibility in treatment. However, researchers caution that bacteria can develop resistance to phages over time, and they are not a universal solution to all infections. While phage therapy holds promise, scientists stress the need for continued research to fully understand how best to use these viruses. Combining phages with antibiotics may offer a more effective strategy for treating antibiotic-resistant infections. As the global challenge of drug-resistant bacteria grows, the development of phage-based treatments is being explored as a potential complement to current medical practices. Researchers are working to expand the library of available phages and improve their application in clinical settings.