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Page: << Prev | 1 | 2 | 3 | Next >> 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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But that's not what happened when he and Chait used doxycycline and Cipro together to fight E. coli. Instead, the more dangerous resistant strain of E. coli got pummeled the hardest, the researchers reported.
"The reason is that, in such cases, although (bacterial) resistance to drug A would indeed diminish the burden imposed by drug A, it also seems to remove its suppressive effect on drug B," Kishony said.
In other words, when drug A -- doxycycline -- was faced with the resistant strain of E. coli, it gave up much of its suppressive effect on drug B, Cipro. And because Cipro was still very effective in killing the doxycycline-resistant strain, this rendered "the combined treatment more effective against the resistant mutant," Kishony said.
The two researchers pointed out that this same combination would probably not work against a Cipro-resistant strain of E. coli. That's because the antagonistic relationship of the two antibiotics is a one-way street, with doxycycline suppressing the effects of Cipro. So, "we do not expect that this particular combination would necessarily select against ciprofloxacin resistance," Kishony said.
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