There are few things more frightening in the world of food safety than becoming infected with the kind of toxic strain of E. coli that has sickened more than 1,500 people in Germany and beyond, but public health officials in the United States cautioned that the bacteria is not as scary as some reports suggest.

"Using terms like ‘mutant killer bacteria’ is irresponsible," said Dr. Timothy Jones, the state epidemiologist in Tennessee. "Bacteria mutate all the time, even the ones we’re comfortable with. And having a strain that is virulent is not unusual."

Of particular concern to officials in the United States have been reports that the European outbreak involves bacteria resistant to antibiotics — not because such reports suggest a particularly dangerous bug, but because they suggest that the Europeans are not looking in the right direction to fight the outbreak.

The accepted medical wisdom in the United States is that E. coli infections should not be treated with antibiotics at all, even if the strain is vulnerable to the drugs. And when a strain shows signs of resistance, treatment with the drugs is a particularly bad idea, said Dr. Phillip Tarr, a professor of pediatrics at Washington University.

"If you give antibiotics and the strain is resistant, then you give that bacteria a competitive advantage to the other bugs in your gut that are susceptible to the drugs, and so it’s an even better environment for the infection," Tarr said.

Yet, to the dismay of U.S. onlookers, European doctors seem focused on the issue of antibiotics and alarmed that they have not found one that works. Professor JoergF. Debatin, the medical director and chief executive of the University Medical Center of Hamburg-Eppendorf, where many of the patients are being treated, said in an interview Tuesday, "There is, as yet, no antibiotics that can treat it."

On both sides of the Atlantic, doctors agree: Patients who suffer bloody diarrhea should be admitted to a hospital and isolated from others because their diarrhea can infect others — a surprisingly common mode of transmission. Toxic E. coli bacteria cause illness by releasing a toxin in the gut that gets absorbed into the bloodstream and injures tiny blood vessels throughout the body. The body responds with clots that clog those vessels. The kidneys, replete with tiny blood vessels, are particularly vulnerable to such clogging and may slow or shut down entirely during a toxic attack, a life-threatening complication.

But the Americans point to studies that show that antibiotics increase the chances of kidney failure while doing little to shorten the duration of infection. Instead of antibiotics, the best treatment is intravenous fluids, which help to keep the kidney functioning, Tarr said.

Most patients infected with toxic E. coli develop painful diarrhea, vomiting and fever within three days. The diarrhea becomes bloody one to three days later and usually resolves within a week of the onset of illness.

U.S. officials were sympathetic to the challenges that European health authorities faced in tracing the source of the outbreak, since such investigations in the United States have been similarly long and confused. The foods involved in the outbreak — tomatoes, cucumbers and lettuce — are often eaten together, and their supply chains can be impossibly complicated to untangle. When a restaurant needs salad fixings, suppliers often mix vegetables from a variety of farms — making a trace to the source close to impossible.

But officials were skeptical that the strain responsible, known as E. coli 0104:H4, would prove to be unique.

"This bug has been seen before," said Dr. Robert Tauxe, deputy director of the division of food-borne, bacterial and mycotic diseases at the Centers for Disease Control and Prevention in Atlanta. That the strain may have genetic material that makes it resistant to antibiotics, however, is intriguing, he said.

"Where has this organism been that it’s been exposed to so much antibiotics that it’s worth its while to be resistant?" Tauxe asked. The answer may influence a growing controversy in the United States over the widespread and routine use of antibiotics to fatten feed animals like pigs.

One clear lesson from the German outbreak is that contaminated food can come from anywhere, said Dr. Michael Osterholm, director of the Center for Infectious Disease Research at the University of Minnesota. "We often want to think that the foods from the developing world are risky," Osterholm said. "Produce safety is a problem everywhere."

Indeed, the German outbreak is likely to increase concerns over the safety of fresh vegetables, Tarr said. The United States has suffered multiple contamination scares over the past decade in tomatoes, lettuce and spinach.

"I can tell you how to make a hamburger safe, but I can’t tell you how to do that with a head of lettuce," Tarr said. "And that’s important."

A law passed by Congress last year gave the Food and Drug Administration new powers to mandate that companies undertake preventive measures to reduce the likelihood of such outbreaks, and the law called for increased inspections to ensure compliance. The agency requested additional financing to implement the new law, including hiring more inspectors next year. Republicans in the House have instead proposed cutting the agency’s budget.