Finally, there’s some good news about the rise of antibiotic-resistant bacteria.  

Bacteria are developing tolerance to nearly all of the antibiotics in modern medicine’s bag, threatening to plunge us back to a time when common bacterial infections killed as doctors helplessly stood by.  

But it turns out that pairing existing antibiotics in new ways can help throttle drug-resistant bacteria. The common antibiotics erythromycin and doxycycline can be used together in a new way to wipe out drug-resistant E. coli bacteria, according to a paper published in the journal PLoS Biology.  


In an effort to make existing antibiotics more effective against drug-resistant bacteria, some doctors are already using “cocktails” of drugs, giving two or more antibiotics at once. In the new study, the researchers instead used just one drug at a time but alternated which was administered over eight doses. 

They were able to wipe out the bacteria in the lab, even though the E. coli was resistant to both drugs individually.

The required doses were also surprisingly low. 

“Research has concentrated for decades on synergistic drug cocktails. We believe ‘sequential synergies’ might be just as potent if we look for them, this research will therefore be of interest to the pharma and dwindling antibiotic discovery communities,” co-author Ayari Fuentes-Hernandez, of the National Autonomous University of Mexico, said in a press statement. 

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Mathematical Thoroughness Turns Up New Possibilities

The researchers tried all of the possible sequences of the two drugs over eight doses.  

“One outcome of this highly surprising result will be to set in motion a series of studies to determine ways of using antibiotics not only in combination, but sequentially and with the potential for lower dosages than is currently thought possible,” co-author Jessica Plucain, of the University of Exeter, said. 

In the laboratory experiment, five different sequences wiped out the bacteria entirely. The doses that researchers would have expected to fail, and therefore contribute to antibiotic resistance, actually reduced the risk of the bacteria developing further resistance.  

The approach may, therefore, help maintain the long-term effectiveness of the antibiotics we have, since few new promising drugs are in the pipeline.

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But there are limits on how much to make of the findings. First, the lab experiment doesn’t factor in how the human immune system might respond to infection and treatment. 

Secondly, there was no obvious reason why some sequences worked better than others, the researchers noted. Some sequences actually resulted in more bacteria growth than the control treatment. 

That means there’s more work to do before the approach can be tried in humans.  

But the findings do mean that antibiotic resistance isn’t as inevitable as scientists may have thought. 

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