MRSA stands for "Methicillin-resistant Staphylococcus aureus". This refers to those strains of the bacteria Staphylococcus aureus (S. aureus) that are resistant to antibiotics of the beta-lactam group (Penicillins, Cephalosporins, etc.). This means that these antibiotics can no longer be used for treatment of MRSA infections.
S. aureus occurs in humans and in animals This bacterium is found in around 30% of the healthy population, without it causing disease symptoms. Skin and mucous membranes are colonised, especially in the area of the nostrils. In contrast, Methicillin-resistant Staphylococcus aureus is found only in less than 1% of the population.
Diseases caused by MRSA
In humans, MRSA can cause purulent infectious diseases (abscesses, boils/furuncles and wound infections) or septicaemia. There is a particular risk of becoming infected with MRSA in cases of chronic diseases, weakened immune system, following operations as well as with wounds and injuries. MRSA is among those germs causing problems in hospitals. Hospital staff are making great efforts to prevent such infections or to identify them early. MRSA may on the one hand originate from the affected patient him/herself (endogenous infections) – the pathogen may, for example, spread from the nostrils onto the skin or into wounds - or on the other, the pathogens may also be transferred from other people or animals or via the inanimate environment.
MRSA on foods
As part of a research project in 2013, AGES selectively tested 100 samples of each of the following: pork, beef, fish and/or shellfish, lettuce/salad and eggs, purchased in retail outlets in the Austrian state of Styria, for MRSA and resistant Enterobacteriaceae.
As part of the test it was possible to isolate MRSA in five of the conventional pork samples and in one of the organic pork samples, in seven of the conventional beef samples and in four of the organic beef samples. MRSA was found in three of the fish and seafood samples tested. MRSA could not be isolated in the content of eggs or in the lettuce/salad samples. As part of testing 200 poultry samples in 2012, MRSA was only found in one turkey meat sample.
Prevalence of MRSA
MRSA is widespread throughout the world. Colonisation with these germs particularly affects patients in hospitals. In addition to the hospital-associated MRSA strains, recent years have seen an increase in the occurrence of strains circulating within the normal population (so-called community-associated MRSA). In the meantime MRSA has also been found to be colonising animals (livestock-associated MRSA); these strains also colonise people in close contact with animals, such as livestock farmers and vets and may cause infections within this population group. These strains still only constitute a small percentage of those MRSA causing infections in humans. However, this percentage is increasingly slowly.
Risk potential of MRSA
MRSA is no more pathogenic than a drug-sensitive Staphylococcus aureus, that means that MRSA does not lead to infections any more frequently. However, the treatment options are limited (number of available antibiotics) which makes treatment of infections more difficult. People with close contact to livestock have increased MRSA colonisation rates. In case of infection in any such person, the possibility of MRSA should be considered from a therapeutic point of view.
Protection against MRSA
MRSA is chiefly transferred from person to person, absolute protection is not possible. To protect against colonisation by MRSA from foods the usual hygiene recommendations apply. Raw meat from all kinds of animals may contain small quantities of MRSA. Heat treated foods such as pasteurised milk, roast or cooked meats are safe. The food should not be contaminated again after heat treatment though. Moreover, meat should always be prepared separately from other raw foods in order to prevent these from becoming contaminated. It is therefore important that when handling raw meat hygiene measures are adhered to strictly. These also provide protection against other infection pathogens such as Salmonella or Campylobacter.
Monitoring the prevalence of MRSA
The MRSA resistance situation is monitored regularly using blood isolates under the coordination of the European Centre for Disease Prevention and Control (ECDC) under the name EARS-Net (European Antimicrobial Resistance Surveillance Network). EARS-Net is an EU-wide human resistance data collection project, in which 40 microbiological laboratories in Austria are participating voluntarily.