June 8, 2010 -- First there were methicillin-resistant Staphylococcus aureus (MRSA) infections. Now there is linezolid-resistant Staphylococcus aureus (LRSA), according to new research in the June 9 issue of the Journal of the American Medical Association.
A relatively new antibiotic, linezolid is considered one of the few effective ways to treat severe MRSA infections, which tend to strike the bloodstream or respiratory tracts of critically ill people in hospitals.
“The main consequence is the risk of losing a very effective and relatively safe drug for the treatment of severe MRSA infection,” study author Miguel Sanchez Garcia, MD, PhD, of the Hospital Clinico San Carlos and Universidad Complutense in Madrid, Spain, says in an email.
Antibiotic resistance, which has been called one of the three greatest threats to human health by the World Health Organization, occurs when bacteria wise up to the presence of an antibiotic and morph into superbugs that can survive and thrive in its presence. The more you use an antibiotic and expose certain organisms to it, the more likely there will be resistance to it.
Garcia and colleagues identified 12 people who developed LRSA infections between April 13 and June 26, 2008, in the intensive care unit of a Madrid-based hospital. The study also showed that linezolid was used extensively in the hospital before the outbreak, which likely played a key role in the development of the resistant strains. As a result, use of linezolid decreased dramatically by July 2008 and no cases have been seen since, the study shows.
LRSA caused ventilator-associated pneumonia in six of the 12 patients and a blood infection in three. The main risk factor for LRSA infection was prior use of linezolid. Six patients died, but only one of these deaths was attributed to LRSA infection, the researchers say.
“In our 12-patient experience, the clinical presentation of the infections was of mild to moderate severity, although they occurred in very debilitated patients,” Garcia says. “In this critically ill population of patients, MRSA infections generally seem to be associated with a more severe clinical course, although it’s too early to say anything definitive about this issue.”
The outbreak was contained with contact isolation to prevent spread and reduction of linezolid use, he says.
But it’s not just Spain. The new findings are generalizable outside of Spain, Garcia says. Cases have been seen in the U.S, Germany, the U.K, Brazil, and Colombia. “Case reports with infection due to linezolid-resistant S. aureus isolates from all parts of the world are increasingly published,” he says. “Most of the cases are associated with prolonged use of linezolid.”
“To put it mildly, this is scary,” saysPhilip M. Tierno Jr., PhD,thedirector of clinical microbiology and immunology at the New York University Langone Medical Center and a clinical professor of microbiology and pathology at the New York University School of Medicine in New York City.
“Previous to this point in time, I have never heard of Staph aureus being resistant to this class of relatively new drugs,” says Tierno, who is author of TheSecret Life of Germs.
Besides linezolid, only drugs like vancomycin are recommended for use in people with severe MRSA infections. “That is the scary part.”
This situation was caused in part by indiscriminate use of antibiotics by doctors, he says. “If there was a judicious application of antibiotics, this would have been more delayed,” he says. “I am hoping this is not widespread.”
Doctors should not shoulder all the blame, he says. Antibiotics are also used indiscriminately in the agriculture setting, he says. Antibiotic resistance is also fostered when people take old antibiotics or finish up a relative or friends’ antibiotic prescription, Tierno tells WebMD.
“We destroyed the gift of antibiotics,” he says.
Robert P. Gaynes, MD, an associate professor of medicine at Emory University School of Medicine in Atlanta, voiced his concerns about overuse of antibiotics in an accompanying editorial.
“It’s really clear that we need to take a careful look at how we are using new antibiotics when we get them,” he tells WebMD. “Antibiotics are always difficult to find, and the number of new ones has dwindled.”
The antibiotic pipeline is dry, he says. “What we have now may be all we ever have,” he says. “In some cases, we are starting to deal with a post-antibiotic era in which there are bacteria that are untreatable with the antibiotics that are available,” he tells WebMD.
“Antibiotics need to be looked at as a medical treasure and a precious, scarce resource and one in which our supply is dwindling,” he says.
The new research is a textbook example of what can happen with antibiotic overuse.
“A new antibiotic was used and in many cases overused, resistance was noted, and that can be generalized to any antibiotic,” he says.