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Worries About an Antibiotic Resistant "Superbug"

A type of bacteria first identified in Chinese pigs now is causing concern in the U.S. due to its resistance to an antibiotic currently seen as a last-ditch effort.

"An E. coli bacterium has been found that has acquired resistance to colistin," says Sankar Swaminathan, MD, the director of the Division of Infectious Diseases for University of Utah Health. "Colistin is an antibiotic that is used to treat some bacteria resistant to multiple antibiotics."

The bacteria were found in a woman in Pennsylvania who had not traveled outside of the U.S. recently. In this case, the patient is fortunate, because the E. coli strain can be treated with other, less toxic antibiotics. But researchers still are concerned about the spread of the gene causing the resistance, due to its potential to spread. "This gene, mcr-1, is on a mobile DNA circle that can be transmitted among bacteria," says Swaminathan. "If mcr-1 becomes more widespread, the potential exists for bacteria that are untreatable by antibiotics."

Gram-negative bacteria are of particular concern for acquiring the mcr-1 mutation. "These are bacteria that commonly reside in the gastrointestinal tract and cause many common infections such as urinary tract infections," says Swaminathan.

So, how did a resistance gene make its way from the fields of China to the U.S.? The answer is, we don't know. However, more is known about how the mutation may have developed. "Because colistin is an old drug, and inexpensive, it has been widely used in agriculture," says Swaminathan. "Antibiotics are used to increase weight gain in animals and to prevent the deleterious effects of intensive factory farming. This highlights the need to reduce unnecessary antibiotic use, not only in medicine but in agriculture."

The reduction of antibiotic overuse is only one part of the solution when it comes fighting bacteria that have developed resistance. After all, there are times when antibiotics are badly needed. As bacteria mutate, new antibiotics need to be developed to fight them. However, development is slow due, in part, to financial issues. "Antibiotics, while invaluable, are not the most profitable drugs for commercial development," says Swaminathan. "Pharmaceutical companies are most interested in drugs that have to be taken every day for the rest of your life."

It may take the government stepping in to make antibiotic research happen, he adds. Legislation is in the works, including federal initiatives to encourage the development of new antibiotics. But it has been slow to pass. "Public support for development of new antibiotics will be helpful," says Swaminathan. "The Infectious Diseases Society of America (IDSA) has been very active in trying to facilitate antibiotic development."