A new, drug-resistant strain of Escherichia coli is causing serious disease, according to a new study published recently in Clinical Infectious Diseases. The authors note that E. coli sequence type ST131 (O25:H4), associated with the CTX-M-15 extended-spectrum β-lactamase, has emerged internationally as a multidrug-resistant pathogen but has received little attention to date in the United States. The strain has been reported in multiple countries and encountered all over the United States. In the study, researchers analyzed resistant E coli isolates collected during 2007 from hospitalized patients across the country. They identified 54 ST131 isolates, which accounted for 67%–69% of E coli isolates exhibiting fluoroquinolone or extended-spectrum cephalosporin resistance. “If we could discover the sources of this strain, the transmission pathways that allow it to spread so effectively, and the factors that have led to its rapid emergence, we could find ways to intervene and possibly slow or halt this strain's emergence,” said study author James Johnson, MD, of the VA Medical Center in Minneapolis. In the past, highly virulent E coli strains usually have been susceptible to antibiotics, although highly resistant strains have been less pathogenic in terms of their ability to cause disease. Now, the study's findings suggest that the ST131 strain has combined a high level of virulence with antimicrobial resistance. “A single E coli clonal group, ST131, probably caused the most significantly antimicrobial-resistant E coli infections in the United States in 2007, thereby constituting an important new public health threat. Enhanced virulence and/or antimicrobial resistance compared with other E coli, plus ongoing dissemination among locales, may underlie ST131's success,” the authors state. “If this strain gains one additional resistance gene,” Dr Johnson added, “it will become almost untreatable and will be a true superbug, which is a very concerning scenario.” See: Clin Infect Dis 2010;51:286–294.