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New research highlights threat posed by MRSA in the community

New research led by MRSA researchers from the University of Bath in collaboration with colleagues in University College Dublin has highlighted the threat posed by the migration of a new, more toxic strain of the bacteria from the United States.

MRSA can be split into two groups, based on where the person became infected. In the UK and Ireland, people typically become infected with MRSA in a hospital environment when they are already sick and have a reduced ability to fight the bacteria.

In the last decade, the emergence of a new type of MRSA capable of infecting healthy people in the community has become a major problem in the United States.

This new study published recently in the Journal of Infectious Diseases explains why hospital acquired MRSA bacteria do not pose a threat in the community by comparing them with the community acquired strain.

Lead author, Dr Ruth Massey from the University of Bath said, “Our research found that the composition of the cell wall of the bacteria is critical to the community acquired MRSA being more toxic and that hospital MRSA strains secrete fewer toxins than strains infecting healthy people in the community.

The ability of the MRSA bacteria to secrete toxins is one of the main ways it causes disease. Using a sensing system, it carefully controls when it switches on its ability to do this, so as not to cause disease until it is firmly established within the human.

Many antibiotics target the cell walls of harmful bacteria, and to resist this, the bacteria have to make changes to their cell wall. We found that the sensing ability of the cell wall in hospital acquired MRSA bacteria is affected by these changes, causing them to reduce the amount of toxins they secrete when antibiotics are present. This means that the hospital strains cannot be both toxic and antibiotic resistant.

However, the newer community acquired MRSA strains infect healthy people, where the composition of their cell walls is different, allowing them to sense their environment and switch toxin expression on at the right time.”

Pictured: Haemolytic activity of the community-associated MRSA strains USA300 LAC on sheep blood agar.

Dr Jim O'Gara, UCD Conway Institute and School of Biomolecular & Biomedical Science, a co-author on the paper added "using clinical isolates of MRSA from an Irish hospital, our experiments showed that antibiotic resistance has a negative impact on toxin production by hospital MRSA strains. The community MRSA strains are antibiotic resistant and more toxic than their hospital counterparts.

Although community MRSA infections have not emerged as a significant public health issue in countries outside North America yet, this new study highlights the importance of research to understand and treat infections caused by these dangerous, and adaptable, pathogens.”

Reference:
Methicillin Resistance Reduces the Virulence of Healthcare-Associated Methicillin-Resistant Staphylococcus aureus by Interfering With the agr Quorum Sensing System.  Justine K. Rudkin, Andrew M. Edwards, Maria G. Bowden et al. Infect Dis. (2012) doi: 10.1093/infdis/jir845 First published online: February 1, 2012