History
An 18-month-old 5.18-kg (11.4-lb) neutered male domestic shorthair cat kept predominantly indoors was evaluated because of lameness and unwillingness to jump of 5 days’ duration. Extensive swelling of the right pelvic limb from the hip region to the digits was evident. A 6-cm-diameter abscess (containing 3 mL of purulent fluid) was present in the lateral and caudal thigh area, affecting the biceps femoris, semitendinosus, and semimembranosus muscles and overlying skin. A foreign body was not identified on surgical exploration of the abscess. The cat's vaccination status was reportedly current, including vaccination against FeLV. Three days later, a second abscess (5 cm in diameter) was detected over the right dorsolateral portion of the sacrum. Surgical exploration of the second abscess revealed similar purulent exudate and absence of a foreign body. Two days later, the swelling in the right limb worsened, and the cat was anorexic and its mentation was obtunded. Given the worsening clinical signs and lack of response to treatment (surgical debridement, drain placement, and antimicrobial administration), the owners elected euthanasia. Treatment likely failed because of the advanced state of disease at the time of veterinary examination and the rapid progression of the disease. The cat was euthanized by IV injection of pentobarbital and submitted to the Utah Veterinary Diagnostic Laboratory for necropsy.
Gross Findings
The cat was in good body and postmortem condition. At necropsy, the skin overlying the right biceps femoris muscle was thick and red and the underlying muscle was pale, friable, and necrotic (Figure 1). Blood-tinged fluid thickened the subcutis, muscle bundles, and tendon sheaths of the entire limb, resulting in severe generalized swelling. There were no other noteworthy gross lesions.
Photograph of the incised right biceps femoris muscle of an 18-month-old predominantly indoor domestic shorthair cat that was evaluated because of lameness and unwillingness to jump of 5 days’ duration. The cat had extensive and progressive swelling of the right pelvic limb from the hip region to the digits. Given the worsening clinical signs and lack of response to treatment, the cat was euthanized. Notice that extensive necrosuppurative myositis is evident.
Citation: Journal of the American Veterinary Medical Association 247, 8; 10.2460/javma.247.8.897
Photograph of the incised right biceps femoris muscle of an 18-month-old predominantly indoor domestic shorthair cat that was evaluated because of lameness and unwillingness to jump of 5 days’ duration. The cat had extensive and progressive swelling of the right pelvic limb from the hip region to the digits. Given the worsening clinical signs and lack of response to treatment, the cat was euthanized. Notice that extensive necrosuppurative myositis is evident.
Citation: Journal of the American Veterinary Medical Association 247, 8; 10.2460/javma.247.8.897
Photograph of the incised right biceps femoris muscle of an 18-month-old predominantly indoor domestic shorthair cat that was evaluated because of lameness and unwillingness to jump of 5 days’ duration. The cat had extensive and progressive swelling of the right pelvic limb from the hip region to the digits. Given the worsening clinical signs and lack of response to treatment, the cat was euthanized. Notice that extensive necrosuppurative myositis is evident.
Citation: Journal of the American Veterinary Medical Association 247, 8; 10.2460/javma.247.8.897
Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page →
Histopathologic and Microbiological Findings
Microscopic examination of affected tissues revealed ulcerative and suppurative dermatitis and necrosuppurative and abscessing cellulitis and myositis, with intralesional colonies of small, rod-shaped, gram-negative bacteria (Figures 2 and 3). Aerobic bacterial culture of affected muscle tissue yielded Serratia marcescens. Bacterial identity was confirmed by results of 16S ribosomal RNA sequencing performed at National Veterinary Services Laboratories, Ames, Iowa. No bacteria were isolated on anaerobic culture of affected muscle tissue.
Photomicrograph of a section of affected right biceps femoris muscle tissue from the cat in Figure 1. There is evidence of suppurative myositis with intralesional bacterial colonies. H&E stain; bar = 30 μm.
Citation: Journal of the American Veterinary Medical Association 247, 8; 10.2460/javma.247.8.897
Photomicrograph of a section of affected right biceps femoris muscle tissue from the cat in Figure 1. There is evidence of suppurative myositis with intralesional bacterial colonies. H&E stain; bar = 30 μm.
Citation: Journal of the American Veterinary Medical Association 247, 8; 10.2460/javma.247.8.897
Photomicrograph of a section of affected right biceps femoris muscle tissue from the cat in Figure 1. There is evidence of suppurative myositis with intralesional bacterial colonies. H&E stain; bar = 30 μm.
Citation: Journal of the American Veterinary Medical Association 247, 8; 10.2460/javma.247.8.897
Photomicrograph of a section of skeletal muscle of the right pelvic limb from the cat in Figure 1. Numerous rod-shaped gram-negative bacteria are visible within the tissue. Tissue Gram stain; bar = 30 μm.
Citation: Journal of the American Veterinary Medical Association 247, 8; 10.2460/javma.247.8.897
Photomicrograph of a section of skeletal muscle of the right pelvic limb from the cat in Figure 1. Numerous rod-shaped gram-negative bacteria are visible within the tissue. Tissue Gram stain; bar = 30 μm.
Citation: Journal of the American Veterinary Medical Association 247, 8; 10.2460/javma.247.8.897
Photomicrograph of a section of skeletal muscle of the right pelvic limb from the cat in Figure 1. Numerous rod-shaped gram-negative bacteria are visible within the tissue. Tissue Gram stain; bar = 30 μm.
Citation: Journal of the American Veterinary Medical Association 247, 8; 10.2460/javma.247.8.897
Morphologic Diagnosis and Case Summary
Morphologic diagnosis: severe, subacute fibrinosuppurative and necrotizing dermatitis, cellulitis, and myositis, with intralesional rod-shaped bacteria.
Case summary: dermatitis, cellulitis, and myositis caused by S marcescens infection in a cat.
Comments
Serratia marcescens is a gram-negative, medium-sized, rod-shaped bacterium in the family Enterobacteriaceae that is saprophytic and widely distributed in the environment (water and soil).1 The bacterium can survive and replicate in adverse environmental conditions, sometimes even in the presence of disinfectant.1 Some serotypes of S marcescens produce prodigiosin, a red pigment. Pigment production is associated with low virulence (environmental origin).2 Serratia marcescens secretes several extracellular products including DNase, proteases, hemolysin, lipase, and lecithinase, which contribute to its pathogenicity, as well as a surfactant that allows the bacterium to adhere to and grow on surfaces.1,2 It is generally considered an opportunistic pathogen and has been associated with nosocomial infections in humans and other animals, especially in immunosuppressed or debilitated patients.2–4
Sporadic opportunistic infections by S marcescens in birds, reptiles, amphibians, and mammals have been reported.5–14 Septicemia as a result of S marcescens infection was diagnosed in an immunosuppressed blue and gold macaw5 and in a swallow-tailed hummingbird.6 Environmental stress and debilitation are believed to have predisposed a dwarf crocodile7 and an amphibian (Ambystoma mexicanum)8 to fatal S marcescens infections. In cows, artificial insemination equipment contaminated with S marcescens is suspected to have caused placentitis and subsequent abortion in 2 animals9 and organic bedding10 contaminated with S marcescens is suspected to have caused an epizootic of mastitis in a large dairy herd.10 In horses, S marcescens infections may cause endocarditis,11 abortion,12 and septicemia.13 Enteritis, icterus, hyperthermia, and death occurred in 14 cats that received S marcescens–contaminated blood transfusions.14 The source of the blood contamination was believed to be the saline solution administered to donor cats receiving tranquilizers IV.14
In veterinary medicine, most cases of abscessing myositis and cellulitis are attributable to direct bacterial inoculation via puncture or bite wounds. Bacteria associated normally with such infections in cats include Pasteurella multocida subsp multocida, Bacteroides spp, Prevotella spp, Prophyromonas spp, Fusobacterium spp, Actinomyces spp, and β-hemolytic streptococci.15 Cases of primary myositis (eg, not due to extension from infected joints or tendons) attributed to aerobic gram-negative bacteria, and specifically S marcescens, are uncommon among humans and other animals. Serratia marcescens was the predominant isolate in several cases of cellulitis in humans following iguana bites,16,17 and there is a single report18 of S marcescens myositis in a human with multiple myeloma. The bacterium caused necrotizing myositis in a kidney transplant recipient also.19
In the cat of this report, it is likely that S marcescens was an environmental contaminant that gained access to the subcutis and skeletal muscle by direct inoculation, such as through a bite wound. The infection was well established prior to the initial evaluation, ruling out a nosocomial infection. The cat was young and lacked known immunosuppressive factors or infections. This case is unique because, to the authors’ knowledge, cellulitis and myositis in a domestic cat due to S marcescens infection have not been reported previously.
References
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