A radical source of antibiotic resistance…

A FEW years ago, a Boston University team headed by Jim Collins published findings that suggested the means by which bactericidal antibiotics result in cell death. Rather than the cause being the cellular target of the drug, the team showed it was the secondary effects of stimulating the production of hydroxyl radicals, a reactive oxygen species 1. The hydroxyl radical is known to cause significant damage to cellular DNA, proteins and cell wall, leading to cell death.

Their 2007 study 1 was initially met with a few raised eyebrows in some quarters, coming in for some criticism for having a few gaps; namely whether the role of the hydroxyl radical was even pertinent in a real world infections settings, which are often in the low-oxygen environment of biofilms 2. There was also some question of whether it was adequately demonstrated that the oxidative stress was a source or the result of cell damage. However, subsequent studies reported by Kohanski, as well as other labs, have described a more defined link between a bactericidal drug and resulting hydroxyl radical formation 3.

In the latest edition of Molecular Cell, a new article from Mike Kohanski, Mark DePristo and Jim Collins reports that prolonged exposure to sub-lethal concentrations of antibiotics can induce multiple drug resistance in E. coli and Staphylococcus aureus strains that were initially drug sensitive 4. E. coli strains were tested with sub-lethal levels of  three major classes of bactericidal antibiotics (quinolone, B-lactam and aminoglycoside), which were found to significantly increase the mutation rate, confirming their expectations.

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