Methicillin-resistant Staphylococcus (MRS) infections are a growing problem in humans and animals. Methicillin is an antibiotic formerly used to treat staphylococcal infections. Most MRS organisms are resistant to all antibiotics in the penicillin and cephalosporin groups, and some are resistant to other antibiotics. A major concern with these infections is the development of strains that will be resistant to all known antibiotics. MRS infections may be localized, like wound infections, or become generalized.

MRS infections are caused by a variety of staphylococcal bacteria. Infections with Staphylococcus aureus (MRSA) and Staphylococcus pseudointermedius (MRSP) are the most common causes in dogs and cats. These organisms may normally live on skin, in the nose, and in the gut of animals without causing any problems. When a wound occurs, a surgical procedure is performed, or skin is otherwise damaged, these bacteria may take advantage of the weak skin and cause an infection. Most Staphylococcus bacteria are susceptible to commonly used disinfectants (bleach) and hand soaps. Transmission is by direct contact with infected people, animals, or via contaminated objects.

Most MRS infections produce pus, fever, decreased appetite and weakness. In humans, MRS infections may resemble spider bites but this does not generally apply to infections in animals. Because animals may carry these bacteria without being sick, it is possible for a wound that is not initially infected with MRS to become infected.

Prognosis is good in most cases when wounds are correctly managed and antibiotic treatment is guided by culture and antibiotic susceptibility testing. Most MRSA infections in dogs and cats are believed to be transmitted to animals from humans. All MRS infections may be transmitted between animals and people, so precautions are needed to prevent such transmission. Hand washing and good hygiene practices are the best preventative measures.


Dr. Allani Delis is a veterinarian at St. Francis Pet Clinic.

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