Staphylococci and MRSA

Staphylococcus aureus (S. aureus) is one of the most common bacteria on the skin and in the nose of humans and animals. Although generally harmless to humans, this bacterium causes (serious) infections when it breaks through the skin barrier. It is sometimes involved in outbreaks of food poisoning. Methicillin-resistant S. aureus (MRSA) is a major problem in healthcare.

Where do Staphylococcus aureus bacteria come from?

Staphylococcus aureus (S. aureus) is a common bacterium on the skin and mucous membranes of humans. Around 20-30% of people are carriers of this bacterium. Although usually harmless to humans, this bacterium causes (serious) infections when it breaks through the skin barrier. Animals (e.g. cattle, sheep, goats) can also contract a S. aureus infection at injection sites or in the case of udder inflammation. In pigs, S. aureus mainly occurs on the skin around the snout and eyes.

What is methicillin-resistant Staphylococcus aureus?

When the Staphylococcus aureus bacterium becomes unresponsive (resistant) to treatment with particular antibiotics, including methicillin, it is referred to as methicillin-resistant Staphylococcus aureus or, in short, MRSA
S. aureus and MRSA, in particular, can give rise to a variety of problems, ranging from skin infections to pneumonia and infections of the bloodstream.

Who gets a S. aureus/MRSA infection?

Anyone can develop a S. aureus infection, although certain population groups are more prone, such as people with chronic conditions (diabetes, cancer, cardiovascular diseases, eczema, lung diseases). In healthcare, the risk of a serious S. aureus infection is greater on account of the patients’ immune system being weakened or because of breaking through the skin barrier during surgical procedures or in the case of (intravenous) catheters.

In healthcare institutions, MRSA is usually transmitted via direct contact with the infected wound or via contaminated hands, e.g. due to inadequate hand hygiene on the part of carers. Asymptomatic carriers (people who are carriers of the bacterium but who do not show any signs of an infection) can also transmit the bacterium to other people.

How can MRSA infections be prevented?

MRSA infections in healthcare institutions can be reduced and prevented via a combination of actions. The most important measure in this regard is hand hygiene, i.e. applying the right hand hygiene technique (disinfect and/or wash hands) at the right time. Furthermore, the early recognition of MRSA carriers (via screening) and decolonization of these carriers (= trying to rid people of MRSA via antiseptic baths) help to prevent further spreading. If a patient tests positive for MRSA, the care personnel are asked to wear gloves and/or an apron for particular care procedures. The doctors are asked to exercise more caution when using or prescribing antibiotics.

What are food-related S. aureus intoxications?

Food poisoning caused by ‘coagulase positive staphylococci (CPS)’ are among the most reported food-related outbreaks in the European Union (see EFSA reports). They are the result of the production of staphylococci enterotoxins in foodstuffs by this bacterium.

What are the symptoms of a food-related S. aureus intoxication?

An intoxication involving staphylococci enterotoxins has a typical incubation period of 2-7 hours, although symptoms may occur as soon as 30 minutes after consumption of a contaminated foodstuff. Poisoning of this kind is characterized by, among other things, vomiting, nausea, stomach cramps and, in some cases, also diarrhea. The severity of the symptoms depends on the quantity and the type of toxins ingested, and the state of health of the individual. Patients usually recover quickly, with the symptoms disappearing within 12 hours, although hospitalization can be necessary for more susceptible individuals (children, the elderly, pregnant women and people with immunity problems). In exceptional cases, food poisoning caused by S. aureus can have a fatal outcome.

How does someone contract a food-related S. aureus intoxication?

People can be carriers of coagulase positive staphylococci (CPS) and thus contaminate food during its preparation. CPS can also be present in non-pasteurized milk and cheese (products) through the use of contaminated milk from animals (cattle, sheep, goats) with udder inflammation. Partly because of their resistance to high salt concentrations, these bacteria can survive and grow in various foods. It is precisely during this growth that the bacterium produces ‘staphylococci enterotoxins’. Although CPS are killed by heating, the toxins resist this treatment, remaining present and active in the food.

How can food-related S. aureus intoxications be prevented?

Instructions regarding the prevention of S. aureus intoxications:

  • hands should be washed carefully before touching and preparing food;
  • do not prepare food if you are sick;
  • in the event of wounds on your hands or wrists, wear gloves while preparing food;
  • if food needs to be kept for longer than 2 hours, keep hot food hot (>60°C) and cold food cold (<4°C);
  • keep the cooling time for food that has been prepared as short as possible.

Sciensano conducts research into the presence of S. aureus, predominantly coagulase positive staphylococci, in our food and closely monitors developments in this area. We develop new detection and typing methods on this basis. In addition, we also coordinate the national surveillance of methicillin-resistant staphylococcus aureus (MRSA) in hospitals and nursing homes, and we monitor MRSA in pigs, chickens and cattle.

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