Antibiotic combinations could fight resistant germs

Using two competing antibiotics against a bacterium -- even when the bug is resistant to one of them -- appears to help conquer the germ and suppress the resistance, new research shows.
The finding is a bit counterintuitive, since for years, doctors have been warning of the overuse of antibiotics, because it encourages germ resistance.

But the new study suggests that sometimes, "antibiotics can be used in suppressive combinations" to limit resistant bacteria, said senior researcher Roy Kishony, an assistant professor in the department of systems biology at Harvard Medical School.

The finding, published in the April 5 issue of the journal Nature, is preliminary and does not have immediate implications for the way doctors use antibiotics. However, the researchers said the study does offer tantalizing new avenues for research.

The advent of antibiotics remains one of the great achievements of modern medicine, credited with saving millions of lives. But the emergence of strains of bacteria that are resistant to nearly all antibiotics has health officials worried.

For example, in 2006, experts warned that methicillin-resistant Staphylococcus aureus (MRSA) had moved from hospital wards to the general community, threatening to become a global epidemic.

And "the issue is broader than MRSA," Dr. Edward Chapnick, director of infectious diseases at Maimonides Medical Center in New York City, told HealthDay at the time. "The issue is antibiotic resistance as a whole. That's not the only resistant organism. It's a big problem, but it's not the only one."

Alarmed by the threat, medical groups and doctors have warned against overusing antibiotics in both humans and animals.

But the Harvard study suggests that combining these drugs in a surprising new way could curb the problem.

In their laboratory experiments, Kishony and Harvard graduate student Remy Chait focused on two strains of the E. coli bacterium -- one that was resistant to doxycycline, a widely used antibiotic, and one that was not.

They exposed the two bacteria to both doxycycline and ciprofloxacin (Cipro), a drug from a different class of antibiotics. Experts call this combination of antibiotics "hyper-antagonistic," because under normal circumstances, doxycycline works to suppress Cipro's germ-killing effects.

Typically, when using antibiotics in combination, any resistant strain should flourish at the expense of strains that had not developed resistance, Kishony explained.

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