New genetic analyzing tool helps trace superbug MRSA’s origins: study
Posted January 21, 2010 7:22 pm.
This article is more than 5 years old.
Researchers have used a “revolutionary” genetic profiling tool to distinguish between closely related strains of the potentially deadly superbug MRSA and even pinpoint when and where in the world the mutated bacteria first arose.
MRSA, or methicillin-resistant Staphylococcus aureus, is a strain of Staph bacteria that is not eradicated by the antibiotics commonly used to treat it.
Most MRSA infections occur in hospitals or other health-care settings, such as nursing homes. Those most at risk are older adults and people with weakened immune systems. But there are also strains typically acquired outside of hospitals. These so-called community-associated MRSA strains can cause serious skin and soft tissue infections, as well as severe pneumonia.
Not only does the genome sequencing equipment help sort MRSA strains that have been transmitted from one continent to another, but it also can determine which strains are infecting patients in one hospital over another or even between wards.
Co-author Dr. Sharon Peacock, a professor of clinical microbiology at the University of Cambridge in England, said being able to better fingerprint strains could help flag transmission hot spots, so measures like frequent handwashing among care providers and environmental cleaning could be beefed up to prevent more patients getting infected.
She said MRSA is a leading cause of hospital-acquired infection worldwide _ and the problem is getting worse.
While national statistics are sketchy in Canada, the United States saw MRSA cases double to 278,000 in 2005 from 127,000 in 1999, with related deaths rising to 17,000 from 12,000 over the same period, she said. In the U.K., there were more than 1,200 MRSA-related deaths in 2008.
Transmission control measures like handwashing and strict hospital-cleaning programs “are driving down rates of infection, but it’s clear that a single intervention will not be enough,” she said.
“I think that this tool will provide extra ammunition to identify routes of transmission for MRSA, so infection control can be concentrated more on areas that appear to be letting MRSA transmit between patients or between hospitals.”
Dr. Michael Gardam, head of infection prevention at Toronto’s University Health Network, said that as a scientist, he finds the research “very interesting.” But he can’t see it changing how hospitals deal with MRSA.
“In terms of the reality we face, which is spreading this stuff around, you fatten the cow by weighing it,” Gardam said. “What I mean by that is we’ve got a problem with MRSA, we’ve gotten a better way of measuring how it’s spread and what it looks like. But that’s not going to stop us from spreading it.”
“So this information will not make people wash their hands more, it’s not going to change the way we design hospitals … it’s not really going to change what I’m doing,” he said, noting that all patients entering the three UHN hospitals are tested for the pathogen.
Still, the British researchers behind the work say the ability to track MRSA’s genetic intricacies will enable scientists to understand how strains of the bacterium _ and other superbugs that may emerge _ can spread so rapidly.
Using the sophisticated DNA sequencing tool, scientists at the Wellcome Trust Sanger Institute in London analyzed more than 63 samples of MRSA.
Of those, 43 came from people in North and South America, Europe, Australia and Asia who were infected between 1982 and 2003. Another 20 came from patients at a single hospital in Thailand who contracted MRSA within seven months of one another.
“We wanted to test whether our method could successfully zoom in and out to allow us to track infection on a global scale _ from continent to continent _ and also on the smallest scale, from person to person,” co-lead author Dr Simon Harris of the Sanger Institute said during a teleconference from London.
Based on the DNA differences among the samples, the researchers were able to construct an evolutionary tree of the superbug. That allowed them to pinpoint the emergence of the dominant global strain of MRSA to Europe in the 1960s _ the same period when widespread antibiotic use began on the continent.
The scientists, who report on their work in this week’s issue of the journal Science, determined that the European strain was behind a MRSA outbreak in Portuguese hospitals in the early 1990s. But a second wave there late in the decade was caused by a strain from Brazil.
A rash of cases in the U.K. in 2003 were caused by a strain that appeared to have originated in Southeast Asia.
“This illustrates how such intercontinental transmissions can result in seriously and sustained waves of hospital infection throughout the country that receives it,” said Harris.
In the Thai hospital, genetic analysis showed patients were infected with two different MRSA strains that had been separately introduced into the facility.
Senior author Dr. Stephen Bentley of the Sanger Institute said the ability to differentiate between isolates is important for developing public-health programs to reduce the number of people infected with and sickened by MRSA.
“It allows researchers and public health officials to see how infections are spread: from person to person; from hospital to hospital; from country to country.”
