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November 7, 2017

How bacteria can defeat antibiotics before they're even discovered

Daily Briefing

    A new study has "turn[ed] the history of [methicillin-resistant Staphylococcus aureus (MRSA)] on its head," showing that bacteria can start developing a resistance to antibiotics they haven't yet encountered, Ed Yong writes for The Atlantic.

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    A complex history

    According to Yong, the history of how MRSA evolved has "become something of a poster child for the superbug threat," demonstrating "how bacteria can quickly evolve to resist a drug that comes into wide use." But the new study, published in BioMed Central, highlights some "glaring plot holes" in the presumed history of MRSA.

    Yong explains how British chemist Alexander Fleming in 1928 discovered penicillin. By 1944, however, scientists had discovered strains of staph that were resistant to penicillin. And according to Yong, these penicillin-resistant strains became increasingly common as penicillin became more widely used. To combat these "incipient superbugs," scientists began using a chemical relative of penicillin, methicillin—but methicillin's efficacy was similarly brief, Yong writes. Just one year after methicillin reached British medical clinics, a researcher, Margaret Jevons, had identified three strains of MRSA.

    Yet while this history of antibiotic discovery, medical use, and resistant bacterium seemed straightforward, Yong continues, there were some complicating factors. For instance, all three strains of MRSA were identified in patients who had not been exposed to methicillin and who had received care at a facility where methicillin had been used only once before. Moreover, MRSA had previously shown up in India and certain Eastern European countries before those regions started using methicillin. 

    Study details

    To address those historical "plot holes," study authors Catriona Harkins and Matthew Holden, both from the University of St. Andrews, sequenced the DNA of over 200 MRSA samples collected between 1960 and 1989. The researchers examined how the strains had evolved over time and found that all the strains had descended from a common ancestor that had developed a methicillin resistance in 1946—13 years before the methicillin was used to treat infections.

    According to the researchers, the findings indicated that "methicillin use was not the original driving factor in the evolution of MRSA as previously thought." Rather, the researchers concluded that the original driving factor was penicillin.

    As Yong explains, mecA, the gene that enables staph to resist methicillin, also can provide resistance to penicillin. As a result, the increased use of penicillin in the 1940s likely fueled an increase in staph strains containing mecA that already were resistant to methicillin, Yong writes.

    The findings undermine traditional thinking on antibiotic resistance, Yong writes, demonstrating that bacteria can start establishing a resistance to antibiotics they have yet to encounter. Further, the study suggests that "new drugs can be neutralized by adaptive genes that are lurking in the environment, waiting for the chance to rise to the occasion," Yong writes—and there's not currently an easily implementable way to predict such unintended consequences of antibiotic use (Yong, The Atlantic, 10/30).

    The current state of hospital antibiotic stewardship


    Antibiotic resistance has emerged as a major imperative for the U.S., linked to an estimated two million infections annually. In response to such concerns—as well as pressure from federal agencies—many hospitals are stepping up their efforts to better manage antibiotic use.

    This survey explores trends in hospital-based antibiotic stewardship programs (ASPs) and identifies what stewardship challenges still remain.

    Get the Survey Results

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