| New Superbug has Criminal Past |
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1 April 2005, for ScienceNOW A deadly bacterium that caused pandemics in the 1950s and '60s has resurfaced, a new genetic analysis shows. The finding closes the case on the origin of the superbug--a meticillin resistant strain of Staphylococcus aureus (MRSA)--and suggests the bacterium may be more dangerous than previously thought. In the 1950s, a new, highly virulent strain of S. aureus, known as phage type 80/81, spread worldwide, causing sepsis, skin lesions, and pneumonia. Although the bug was resistant to penicillin, scientists finally stamped it out in the 1960s with a new class of antibiotics, including meticillin. In the 1990s, meticillin-resistant strains of S. aureus emerged, leaving only one antibiotic, vancomycin, as a last line of defense. Initially, the MRSA strains spread primarily through hospitals, but in the late 1990s, outbreaks began in the wider community. Researchers thought these community strains could be hospital escapees, but a genetic analysis showed they had distinct origins from the hospital strains. Now it turns out that one of the most prevalent community MRSA strains, called southwest Pacific (SWP), is a revamped version of 80/81. A team led by microbiologist Mark Enright, of the University of Bath in the United Kingdom examined samples of 80/81 collected worldwide in the 1950s and 60s and sequenced 15 genes essential for processes within the organism. Compared with SWP, "the only difference, really, is the meticillin-resistance gene," Enright says, which shows that SWP is a retooled version of 80/81. The researchers, who report their findings 2 April in Lancet, say there were two major steps in the lineage's evolution: First S. aureus acquired the gene for the Panton-Valentine leukocidin toxin, becoming the virulent 80/81 strain. Then, sometime after the introduction of meticillin-like antibiotics, the bug acquired genes to resist those drugs, becoming the SWP strain. But it is still a mystery where it was before arising again, and why it made a comeback in the 1990s."Since SWP came from 80/81, one has every reason to be concerned about the resurfacing of this bacterial lineage," says microbiologist Alexander Tomasz of Rockefeller University in New York City. "It needs to be carefully watched." |