Using viruses instead of antibiotics to tame troublesome drug-resistant bacteria is a promising strategy, known as bacteriophage or "phage therapy." Scientists at the National Institutes of Health have used two different bacteriophage viruses individually and then together to successfully treat research mice infected with multidrug-resistant Klebsiella pneumoniae sequence type 258 (ST258). The bacterium K. pneumoniae ST258 is included on a CDC list of biggest antibiotic resistance threats in the United States. High rates of morbidity and mortality are associated with untreated K. pneumoniae infections.