Superbug strikes again
Alternative antibiotics offer slim comfort as potent strain returns.
11 October 2002
HELEN PEARSON
A drug-resistant superbug has resurfaced, doctors announced today, leaving researchers scrabbling for the next line of antibiotic defence.
The rogue Staphylococcus aureus bacteria, identified in the foot ulcer of a Pennsylvania patient, are resistant to vancomycin, one of the last lines of antibiotic defence1.
More cases were widely anticipated after reports of the first such strain earlier this year2.
Today's announcement coincided with confirmation of the case by the US Centers for Disease Control and Prevention in Atlanta, Georgia.
The finding fuels an intensifying search for next-generation drugs to control life-threatening hospital infections. Michael Rybak and his colleagues at Wayne State University in Detroit, Michigan, recently tested the first vancomycin-resistant S. aureus (VRSA) strain, taken from a Michigan patient's wounds, against some of the newest antibiotics in the drugs arsenal.
Two drugs, daptomycin, which is under development, and the recently released quinupristin-dalfopristin, killed more than 99% of the bacteria, the researchers found. "It gives us a little level of comfort," says Rybak. He presented his results at the Interscience Conference on Antimicrobial Agents and Chemotherapy in San Diego late last month. Linezolid, another relatively new antibiotic, only curbed the growth of VRSA, they found.
Rybak and his team mimicked severe infection in a wound by growing high concentrations of VRSA in a matrix like a blood clot. They treated these for three days with doses equivalent to those given to patients.
"It is reassuring," says George Eliopoulos, who studies antibacterial agents at Harvard Medical School in Boston, "but I wouldn't breathe a total sigh of relief." He is concerned that the bacteria will also acquire resistance to the new drugs. S. aureus strains immune to linezolid and quinupristin-dalfopristin have already been reported, despite both being used for less than three years.
Bacteria may find it harder to fight daptomycin, however, because it operates in a different way to many standard antibiotics. Rather than stopping bugs growing, daptomycin kills them by puncturing the cell membrane and letting the contents leak out. "Resistance will emerge but it won't be soon," predicts Frank Tally of Cubist Pharmaceuticals in Lexington, Massachusetts, which licenses the drug.
Cubist Pharmaceuticals plans to file an application for daptomycin's approval with the Food and Drug Administration this year. This might be rubber-stamped by the end of 2003 at the earliest. "There's clearly a need for it to be fast-tracked," says David Snydman who has carried out studies on the drug at the Tufts University School of Medicine in Boston, Massachusetts.
According to Snydman, daptomycin is by far the most promising of the antibiotics being developed to tackle VRSA. Even so, he says, if the bacteria beat the drugs "we're gonna have a major problem".
References
CDC: Vancomycin-resistant Staphylococcus aureus - Pennsylvania, 2002. Morbidity and Mortality Weekly Report , 51, 902, (2002). |Homepage|
CDC: Staphylococcus aureus resistant to vancomycin - United States, 2002. Morbidity and Mortality Weekly Report , 51, 565 - 567, (2002). |Homepage|
