Antibiotic resistant bacterial infections

MRSA (Meticillin Resistant Staphylococcus aureus) is a nasty bacterial infection that has been widely reported in the media. It has been in the news for the sometimes fatal infection of people and has been dubbed ‘the superbug’ and ‘flesh eating bacteria’. MRSA can also occur in pets; however, dogs more commonly can be infected with a different, although similar infection: MRSI (meticillin resistant Staphylococcus intermedius) or MRSP (meticillin resistant Staphylococcus pseudointermedius).

MRSA (Meticillin Resistant Staphylococcus aureus) is a bacterium that is resistant to the antibiotic meticillin (which is a type of penicillin). The earliest recorded MRSA was identified in humans in the UK in 1961. It was first reported to be a major problem in human hospitals in the USA in the 1970s, and in the 1990s it became recognised as an important cause of hospital associated infection in human hospitals all over the world. These hospitals acquired strains of MRSA (HA-MRSA) cause the majority of human infections.

The skin is commonly home to huge numbers of bacteria that do not normally cause any problems. Staphylococcus is one of these bacteria. All people and animals carryStaphylococcus bacteria on their skin as part of their normal body flora, and as many as three in a hundred (3%) people carry the MRSA bacteria without realising or having any problems as a result. Figures also suggest that between two and nine in a hundred (2-9%) dogs and one in a hundred (1%) cats are carriers of MRSA in the UK.

MRSA is spread by direct contact between infected people and animals. MRSA can be spread from people to animals and less frequently from animals back to people. It can also be picked up from contaminated objects in the environment such as towels, bedding and medical equipment.

Based on clinical cases observed, many experts believe companion animals are generally transient carriers of MRSA, which means they may only carry the bacteria for about 2-3 weeks before the bacterial population disappears. If you can avoid contact with your pet during this time and wash your hands regularly after touching them it should be possible to protect yourself against infection.

MRSP (meticillin resistant Staphylococcus pseudointermedius) is also a bacteria that is resistant to the antibiotic meticillin. Healthy animals can carry MRSP, and it is common on the skin and in the nose of healthy dogs. MRSP infections in people are very rare and so spread of MRSP to pets is usually from direct contact with an infected animal.

Being colonised with MRSA or MRSP may present no problems for the host. These bacteria are most likely to cause disease if they are able to get onto an animal that is already sick, has a wound or whose immune system is compromised (whether by disease or drug treatment, e.g. chemotherapy). MRSA infection in UK pets is relatively rare.

If a healthy dog living in a household where an individual is discovered to be carrying an antibiotic resistant infection then it is best to isolate the pet from that household until they are cleared of the bacteria. This usually happens just with time, but active decolonisation (removal of the bacteria from the skin) can be achieved by baths in chlorhexidine shampoo and topical antibiotic treatment into the nose.

Detection of the bacteria on a swab from your pet’s skin surface does not mean they are infected with the bacteria. Indeed it is not unusual to find antibiotic resistant bacteria on the skin of apparently healthy animals. These bacteria can be acquired from a visit to a hospital or veterinary hospital (where antibiotic resistant bacteria are more prevalent than in the “normal” environment) or by direct contact with a carrier or infected individual human or other animal.

Animals that share their home with people at high risk of exposure to MRSA, i.e. healthcare workers, veterinary professionals and those who are immunocompromised, have been reported to be more at risk of becoming infected with antibiotic resistant bacteria.

If you are carrying MRSA you may not know provided you remain otherwise healthy. Infected people may have skin signs such as infections and spots and more severe cases occur in wounds after surgery. It is not possible to tell what is causing a wound infection just by looking at it. To make a diagnosis your vet or doctor would need to take a swab from an infected area and send this away for culture and identification in a laboratory.

Since Staphylococcus bacteria are most commonly found on the skin this is where infection tends to occur. If your pet has a longstanding skin infection (which may appear as itchiness, pustules, boils or ulcers), particularly if this does not respond to routine antibiotics from your vet, you should be consider the possibility of an antibiotic resistant infection.

Although relatively rare in pets, MRSA and MRSP infections can cause severe infections and sepsis which may result in death.

When animals are colonised with MRSP without obvious clinical signs there are no recognised methods for removing the resistant bacteria from them. You must take good care with hygiene and hand washing. Faeces may carry the infection so ensure you pick up any excrement immediately and dispose of it before other animals can come into contact with it. Although MRSP does not survive well in the environment, you should wash your pet’s bedding separately and if possible dry it in a tumble drier to decontaminate it. There are some instances, however, where dogs may remain as carriers of MRSP for prolonged periods of time.

In cases of skin infections – the most common type of infection found in animals – an option may be either applying antibiotic cream to the skin infection, treat the animal with other antibiotics, or a combination of both. Your veterinarian will determine the appropriate treatment for your animal. If you have to handle infected wounds make sure you wear gloves and dispose of contaminated gloves and bandaging appropriately (your vet will be able to advise you on this).

Both MRSA and MRSP infections are resistant to a number of widely used antibiotics, meaning it can be more difficult to treat than other infections. However, despite the media portrayals most MRSA and MRSP infections can actually be successfully treated.

When faced with antibiotic resistant bacteria it is essential to identify which antibiotics are effective, your vet will need to take swabs and may need to take advice from drug or infectious disease specialists to choose the right treatment. In addition, good hygiene is essential, e.g. cleaning and washing of the wound can be helpful as these bacteria like to live in dirty, enclosed environments where oxygen levels are low.

Antibiotic resistance occurs when strains of bacteria change (mutate) and become resistant to specific antibiotics. Antibiotics may also destroy the normal flora of the body, such that resistant bacteria have the chance to multiply in numbers. In addition, the overuse of antibiotics, e.g. using antibiotics to treat minor conditions and not finishing a recommended course of treatment may also promote antibiotic resistance.

The veterinary world has the chance to learn many lessons from what has happened in human medicine. It is important that we protect the antibiotics that we have and ensure that they can still serve us well in the future. If you are prescribed any antibiotics for your pet make sure you follow your vet’s advice exactly and always finish the course of antibiotics – even if your pet seems better.

Further information on MRSA and MRSP in pets, including how to manage an infected pet, is available on the Bella Moss Foundation website and on the BSAVA website