Surgery STAT: Managing methicillin-resistant wound infections
Jan 01, 2010
In dogs, Staphylococcus pseudintermedius (formerly recognized as S. intermedius) is the most common resident organism of the skin and the most common cause of canine pyoderma. Occasionally, S. pseudintermedius and related species (S. intermedius, S. schleiferi) acquire a genetically coded, penicillin-binding protein that confers resistance to all beta-lactam antimicrobials and their derivatives. Affected organisms are termed methicillin-resistant Staphylococcus. In older articles, these organisms were known as MRSI; however, the term MRSP is now considered more appropriate.
Healthy dogs and people can serve as carriers for MRSP. In one reported outbreak of surgical wound infections in pets, MRSP carriage was detected in a surgeon, two surgical nurses, and staff members' dogs that were frequent visitors to the clinic. Colonized personnel were likely the source of postoperative wound infections. Almost half of owners of dogs with MRSP deep pyoderma are colonized with the same bacteria. Infections within humans, however, are rare.
Systemic antimicrobials should be based on results of culture and susceptibility testing; however, some strains of MRSP may display in vitro susceptibility that does not correlate with in vivo response. Microbiology personnel can be contacted to determine the most common sensitivity pattern of local strains while results are pending. In our hospital, MRSP is usually susceptible to chloramphenicol (100 percent) or aminoglycosides (97 percent). Systemic antimicrobials should be administered at least one week beyond remission of clinical disease (usually a minimum of 21 days). Repeated antimicrobial exposure at subtherapeutic concentrations or inappropriately short duration may select for resistance. In some patients, topical wound therapy is sufficient to clear the infection. Deep tissue cultures should be repeated during antibiotic therapy if healing is not progressing as expected.
If an outbreak of MRSP wound infections is detected in your hospital, evaluate your hand hygiene and surgical preparation practices. Updating these practices will provide the best method for preventing future infections.
Dr. Karen Tobias is an ACVS board-certified veterinary surgeon and professor of small-animal surgery at the University of Tennessee. She is the author of Manual of Small Animal Soft Tissue Surgery (Wiley-Blackwell, 2009), and the owner of several incorrigible pets.