A U.S. research team has found drug-resistant strains of E.coli and Klebsiella bacteria in more than 50 blood, urine and respiratory samples.

The University of Texas Health Science Center at San Antonio said the bacteria, thought to be rare in the United States, was found in hospital and non-hospital clinical settings between 2000 and 2006.

Pathologist James Jorgenson said the drug-resistant strains produce extended-spectrum beta-lactamases (ESBLs), enzymes that destroy penicillin or cephalosporin class drugs, the university said in a release.

The strains, which resemble bacteria reported in Latin America, Asia and Europe, are also typically resistant to other commonly used antibiotic drug classes. "These very common bacteria, when they produce these enzymes, are much harder to kill with antibiotics," Jorgensen said.

Copyright 2008 by United Press International