More Bacteria Resisting Antibiotics : Health: Scientists say the problem is widespread in some parts of the world and could become a serious concern in the United States.

In a recent study, researchers in Seattle found antibiotics highly effective in preventing persistent urinary tract infections in all but two young women they studied.

Laboratory tests uncovered the apparent reason for the two exceptions. Both women harbored infection-causing bacteria in their systems that were resistant to antibiotics, making the drugs unable to kill the bacteria.

The incident was just one example of a problem scientists say already is widespread in some parts of the world and could become a health care headache in the United States: the genetic evolution of bacteria that can resist the effects of antibiotics, a class of drugs that kill bacteria and slow their growth.

Researchers at Brigham and Women’s Hospital in Boston who recently compared antibiotic resistance levels among children in the United States, Venezuela and China found reason both for hope and concern.

On the hopeful side, they found a relatively high proportion of children they tested in Boston did not have bacteria in their systems that were antibiotic-resistant. They said that was a good sign that the strict controls on antibiotic use can reduce the problem.

But they found a very different situation among the children in Venezuela and China, where antibiotic use is largely unregulated. Only one of 41 children studied in Caracas, Venezuela, and two of 53 children in Quin Pu, China, near Shanghai, had no resistant bacteria in their feces.

The Venezuelan children ranged in age from 5 months to 5 years and the Chinese children from 6 months to 6 years. In contrast to them, 18 of the 39 Boston children tested--who were 3 and under--had no resistant bacteria.

The researchers also found that 20% of the Venezuelan children and 6% of the Chinese children harbored bacteria resistant to five or more types of antibiotics--but none of the Boston children.

They said they used children in the study because they were less likely than adults to have received repeated doses of antibiotics and had less lifetime exposure to resistant bacteria.

Their findings confirm scientists’ suspicions that antibiotic resistance is a serious public health problem in developing countries, and at the moment, one of greater dimensions than in the United States, said Dr. Thomas O’Brien and Dr. Susan Lester, who conducted the study.

In developing countries, “it is much harder to get antibiotic usage controlled,” said O’Brien, adding that “the impact of resistance also is worse in developing countries. In the United States, you can usually find an expensive new antibiotic to overcome resistance.”

But before Americans become complacent about the study results, O’Brien and Lester said they should consider another aspect of the findings, which showed that although nearly all of the Chinese and Venezuelan children had resistant strains of the common intestinal bacteria Escherichia coli, nine of the Venezuelan children and 15 of the Chinese children had never been given any antibiotics.

That indicates that “your own personal use of antibiotics does not determine” whether you are likely to have resistant bacteria, said Lester, whose study appeared in The New England Journal of Medicine. Resistance is “more correlated with where you live, since you can’t help acquiring bacteria” from a variety of sources, including food. They said the fact that bacteria do not recognize national boundaries and there are already signs--that antibiotic-resistant strains are spreading throughout the United States, should underline for doctors and patients alike the importance of using antibiotics with restraint.