'Combining 4 or 5 antibiotics may effectively kill bacteria'

Scientists say they have discovered thousands of four- and five-drug combinations of antibiotics that are more effective at killing harmful bacteria than thought.

The findings, published in the journal npj Systems Biology and Applications, could be a major step towards protecting public health at a time when pathogens and common infections are increasingly becoming resistant to antibiotics.

"There is a tradition of using just one drug, maybe two," said Pamela Yeh, an assistant professor at the University of California, Los Angeles (UCLA) in the US.

"We are offering an alternative that looks very promising. We shouldn't limit ourselves to just single drugs or two-drug combinations in our medical toolbox.

"We expect several of these combinations, or more, will work much better than existing antibiotics," said Yeh.

Working with eight antibiotics, the researchers analysed how every possible four- and five-drug combination, including many with varying dosages -- a total of 18,278 combinations in all -- worked against E coli.

They expected that some of the combinations would be very effective at killing the bacteria, but they were startled by how many potent combinations they discovered.

For every combination they tested, the researchers first predicted how effective they thought it would be in stopping the growth of E coli.

Among the four-drug combinations, there were 1,676 groupings that performed better than they expected.

Among the five-drug combinations, 6,443 groupings were more effective than expected.

On the other hand, 2,331 four-drug combinations and 5,199 five-drug combinations were less effective than the researchers expected they would be, said Elif Tekin, a postdoctoral scholar UCLA.

Some of the four- and five-drug combinations were effective at least partly because individual medications have different mechanisms for targeting E coli.

The eight tested by the researchers work in six unique ways.

"A whole can be much more, or much less, than the sum of its parts, as we often see with a baseball or basketball team," Yeh said.

She added that although the results are very promising, the drug combinations have been tested in only a laboratory setting and likely are at least years away from being evaluated as possible treatments for people.