Haematogenous polyostotic osteomyelitis caused by Serratia marcescens in a cat

A 2-year-old female Bengal cat was referred for acute right forelimb lameness one month after ovariectomy. Physical examination revealed multifocal pain on bone palpation and fever. Radiographs showed mixed lytic-proliferative polyostotic diaphyseal osteopathy of multiple bone segments. Histopathologic evaluation of bone biopsies showed severe chronic pyogranulomatous osteomyelitis and multidrug-resistant Serratia marcescens was cultured. Antibiotic therapy with piperacillin-tazobactam was administered for 60 days, based on susceptibility testing. Lameness and bone pain resolved within 15 days, and radiographs after 30 days showed decreased bone lysis. At a 6-month recheck, the cat recovered completely, and only bone remodelling was evident on radiographs. Multifocal bacterial haematogenous osteomyelitis (HO) caused by Serratia marcescens was diagnosed in an adult immunocompetent cat. HO is infrequently reported in dogs and cats with young and immunocompromised patients being most at risk. Prior ovariectomy and anaesthesia may have predisposed the cat to the development of a hospital-associated infection (HAI), as other aetiologies or predisposing causes for osteomyelitis were reasonably excluded. Serratia marcescens is a gram-negative bacterium recently reported as responsible for human and veterinary HAIs, although it has never been stated for HO in small animals. Early recognition and antibiotic therapy led to good outcome in this case.