SAN FRANCISCO -- September 15, 2009 -- A worldwide survey of susceptibility of drugs used to treat intra-abdominal infections caused by Escherichia coli found wide-ranging differences, researchers said here at the 49th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).

"We found that extended-spectrum beta-lactamase-producing E coli which can make several classes of antibiotics ineffective varies from as low as 2.7% in North America to about 30% in South America and Asia," said Maria Villegas, MD, CIDEM Research Clinic, Cali, Colombia.

"What this means is that doctors have to be very careful which antibiotics they prescribe for patients with E coli infection," she said on September 14 during a poster presentation. "If you have a person who is in generally good health and you select a drug that is ineffective, you may have the opportunity to determine which antibiotic will work. But if that patient is critically ill, you really have only 1 chance to select the best drug."

Dr. Villegas reported results of the Study for Monitoring Antimicrobial Resistance Trends (SMART), which has been tracking global susceptibility and epidemiologic patterns of intra-abdominal infections since 2002.

"With extended-spectrum beta-lactamase-producing E coli rates increasing in many regions, it is important to know local prevalence," said lead author Robert Badal, International Health Management Association, Inc., Schaumburg, Illinois.

The 2008 SMART data was collected from 116 sites in 44 countries. Each of the sites sent as many as 100 consecutively isolated Gram-negative pathogens from intra-abdominal infection to a central laboratory, which confirmed identifications and performed and interpreted susceptibility testing. The researchers examined 3,093 E coli isolates.

Overall, 19.4% of the samples expressed extended-spectrum beta-lactamase-producing E coli. About 30.6% of the samples from Latin America, 28.8% of samples from Asia and the Pacific, 17.6% of samples from the Middle East, 14.5% of samples from Europe, 4.8% of samples from Africa and 2.7% of samples from North America were determined to be extended-spectrum beta-lactamase-producing E coli.

Badal said the drug interaction indicated that almost all the extended-spectrum beta-lactamase-producing E coli samples were susceptible to ertapenem, imipenem, and amikacin virtually worldwide. On the other hand, ampicillin-sulbactam -- once the standard of care for treatment of E coli infection -- was less than 50% effective against extended-spectrum beta-lactamase-producing E coli (60% in North America).

"You really have to know your local epidemiology," Dr. Villegas said. "The wide disparity between the susceptibility of extended-spectrum beta-lactamase–negative E coli strains and extended-spectrum beta-lactamase-producing E coli to non-carbapenem drugs in this study necessitates understanding of local prevalence data to help guide empiric therapy."

"Knowledge of isolates' extended-spectrum beta-lactamase status is critical to effective therapy of these infections, as some extended-spectrum beta-lactamase-producing E coli may appear falsely susceptible to some cephalosporins," said Dr. Badal