Biologists have identified over 8,000 new combinations of antibiotics that are surprisingly more effective at killing harmful bacteria than the prevailing ones.

Scientists have traditionally believed that combining more than two drugs to fight harmful bacteria would yield diminishing returns. The prevailing theory is that the incremental benefits of combining three or more drugs would be too small to matter, or that the interactions among the drugs would cause their benefits to cancel one another out.

However, the study discovered over 8,000 combinations of four and five existing medications that are effective, a finding that could be a major step toward protecting public health at a time when pathogens and common infections are increasingly becoming resistant to antibiotics, the researchers said.

"I was blown away by how many effective combinations there are as we increased the number of drugs," said Van Savage, the Professor at the University of California - Los Angeles (UCLA). "People may think they know how drug combinations will interact, but they really don't." For the study, reported in the journal npj Systems Biology and Applications, the team looked at eight common antibiotics and analysed how every possible four to five drug combination, including with varying dosages, worked against E-coli.

The combinations were effective because individual medications have different means of targeting E. coli. "Some drugs attack the cell walls, others attack the DNA inside," Savage said. "It's like attacking a castle or fortress. Combining different methods of attacking may be more effective than just a single approach."

"There is a tradition of using just one drug, maybe two," said Pamela Yeh, Assistant Professor at the UCLA. "We're 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," Yeh added. However, Yeh noted that although the results are very promising, the drug combinations have been tested in only a laboratory setting and are at least years away from being evaluated as possible treatments for people.