Clinical, microbiological, and molecular characterization of methicillin-resistant <italic>Staphylococcus aureus</italic> infections of cats

1421 B of the genus Staphylococcus are members of the commensal cutaneous and mucosal microflora of cats. Coagulase-positive species, such as Staphylococcus intermedius, Staphylococcus hyicus, and Staphylococcus aureus, and several coagulase-negative species have been isolated in microbiological surveys of skin and mucous membranes in healthy cats. Because household cats are more frequently colonized by coagulase-positive staphylococci than are those living in catteries, transmission from humans has been suggested. When cutaneous or systemic disease disrupts defense mechanisms of the skin’s surface, bacterial infection (pyoderma) or otitis externa may result from these same staphylococcal species. Invasive infections involving the genitourinary tract, respiratory tract, joints, and body cavities may also result by ascension along epithelial tracts, introduction via penetrating wounds, or hematogenous spread. The coagulase-positive species are the most common causes of staphylococcal infections in cats, and information is lacking regarding the pathogenicity of coagulase-negative staphylococci. However, coagulase-negative staphylococci are receiving renewed attention with regard to their medical importance in humans and cats. Isolates of MRSA are associated with nosocomial and community-acquired infections in humans, and some strains may cause more severe clinical signs than are seen with infections attributable to MSSA isolates. Domestic animals, including cats, are reportedly also susceptible to MRSA infections, and concerns that companion animals may serve as reservoirs of MRSA have been emphasized in several reports. To our knowledge, clinical descriptions of MRSA infection or analysis of the microbiological and molecular characteristics of a large series of MRSA isolates obtained from cats has not been reported. The purposes of the study reported here were to describe the clinical, microbiological, and molecular characteristics of MRSA infections of cats. We hypothesized that MRSA infections of cats would cause more severe clinical signs than would be seen with MSSA infections, such as deeper tissue invasion, increased degree of tissue injury, and increased morbidity and mortality rates. We also hypothesized that genetic analysis of isolates obtained from cats would reveal Received January 16, 2006. Accepted February 22, 2006. From the Departments of Clinical Studies–Philadelphia (Morris, Mauldin, Shofer) and Pathobiology (Mauldin, O’Shea, Rankin), School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104. Address correspondence to Dr. Morris. Clinical, microbiological, and molecular characterization of methicillin-resistant Staphylococcus aureus infections of cats