Hospital screening tests are failing to identify the true extent of microbial resistance, according to new research. Scientists have found that disease-causing bacteria carry antibiotic resistance genes that are dormant as a result of a genetic mutation. During screening, the bacteria appear susceptible to antibiotics. But such mutations easily become lost, rapidly transforming the bacteria into drug-resistant strains – dramatically increasing the risk that the drug therapy will fail. The study, led by the University of Leeds, reveals another layer in the complex scientific fight to understand and combat one of the biggest challenges facing modern healthcare: the rise of drug-resistant superbugs.