New MRSA variant detected in cow's milk that can evade some existing detection methods

June 02, 2011

An Article published Online First by The Lancet Infectious Diseases reports detection of a new variant of meticilin-resistant Staphylococcus aureus in cow's milk--genetically different to existing MRSA strains--from the UK and Denmark. This new variant is associated with clinical disease in people, yet some existing testing methods would wrongly identify this new variant as meticillin-susceptible, leading to prescriptions of the wrong antibiotics. Furthermore, the study reveals indirect evidence that cows could be a reservoir of MRSA that could infect humans. The study is by Dr Mark A Holmes, Department of Veterinary Medicine, University of Cambridge, UK, and colleagues.

The resistance found in variants of MRSA is usually conferred by the mecA gene, which can be transferred between S. aureus strains. In today's era of genetic testing, a positive test for the mecA gene has become the gold standard for identifying an MRSA. But in this study, Holmes and colleagues found an MRSA with a new mecA gene (a mecA homologue) that was not detected by the usual confirmatory test for mecA. The authors say that, when existing detection methods such as the polymerase chain reaction (PCR) or monoclonal antibody methods are used as the only method to detect MRSA, or when these methods are used to confirm provisional detection of MRSA, then the new variant will be wrongly diagnosed as meticillin-susceptible.

The study also shows indirect, although not conclusive, evidence that cows could be an important reservoir of this new-variant of MRSA infection in humans. Firstly, the isolates found in humans were either of a strain thought to be unique in animals or other strain types detected in cattle but not previously in humans. Secondly, none of the strain types come from lineages previously associated with human MRSA carriage or infection. Thirdly, in England, where data from both cattle and human beings are available, there is evidence of geographical association between human and bovine isolates (human and bovine ST425 in the southwest, human and bovine ST130 in the east, and human and bovine ST1526 in the northeast). Finally, the UK Veterinary Laboratories Agency survey looking for MRSA in dairy cattle noted no other (ie, human) MRSA.

The authors say "Such evidence suggests that a bovine reservoir exists, from which mecALGA251 MRSA is transmitted to people. Pasteurisation of milk will prevent any risk of infection via the food chain but individuals in close contact with cattle could be at higher risk of carriage. Further research is needed to test this hypothesis."

They add: "The discovery of this previously undetected mecA homologue is potentially of public health importance. Diagnostic protocols, whether for clinical or epidemiological purposes, should consider the ramifications of not detecting S aureus strains that carry this new mecA homologue."
Dr Mark A Holmes, Department of Veterinary Medicine, University of Cambridge, UK. Please contact Genevieve Maul, Media Relations. T) +44 (0) 1223 765542 / +44 (0) 7774 017464. E)


Related MRSA Articles from Brightsurf:

Widely available antibiotics could be used in the treatment of 'superbug' MRSA
Some MRSA infections could be tackled using widely-available antibiotics, suggests new research from an international collaboration led by scientists at the University of Cambridge and the Wellcome Sanger Institute.

Computer model shows how to better control MRSA outbreaks
A research team led by scientists at the Columbia University Mailman School of Public Health report on a new method to help health officials control outbreaks of methicillin-resistant Staphylococcus aureus, or MRSA, a life-threatening antibiotic-resistant infection often seen in hospitals.

Using MRSA's strength against it
MRSA evolved to become a deadly killer because it's wily and resilient.

Livestock-associated MRSAfound among MRSA from humans
The survey results show more frequent detections and geographical dispersion of LA-MRSA in humans in the EU/EEA since 2007, and highlight the public health and veterinary importance of LA-MRSA as a 'One Health' issue.

Fighting MRSA with new membrane-busting compounds
Public health officials are increasingly concerned over methicillin-resistant Staphylococcus aureus (MRSA).

Know thy enemy: Kill MRSA with tailored chemistry
UConn medicinal chemists have developed experimental antibiotics that kill MRSA, a common and often deadly bacteria that causes skin, lung, and heart infections.

MRSA uses decoys to evade a last-resort antibiotic
The superbug MRSA uses decoys to evade a last-resort antibiotic, reveals new research.

Scientists find a salty way to kill MRSA
Scientists have discovered a new way to attack Staphylococcus aureus bacteria.

Experimental antibiotic treats deadly MRSA infection
A new experimental antibiotic developed by a team of scientists at Rutgers University successfully treats the deadly MRSA infection and restores the efficacy of a commonly prescribed antibiotic that has become ineffective against MRSA.

OU team develops new antibiotic to fight MRSA
A University of Oklahoma team of chemists has developed a new antibiotic formulation to fight the sometimes deadly staph infection caused by methicillin-resistant S. aureus or MRSA and other antibiotic-resistant infectious bacteria.

Read More: MRSA News and MRSA Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to