Human isolates of Staphylococcus caprae: association with bone and joint infections

Staphylococcus caprae is a coagulase-negative, DNase-positive member of the genus Staphylococcus usually associated with goats, but since 1991 a few laboratories have reported isolating the organism from human clinical specimens. We report on the isolation of 14 strains from human specimens and note that 10 strains were obtained from patients with bone and joint infections. Nine of the 10 infections started with traumatic fractures, and the other was a case of mastoiditis. Seven of these 10 infections were in patients with orthopedic prostheses, which appears to be a risk factor. Three of the 14 strains were from transplant patients. For three of the patients, S. caprae was the only organism isolated. S. caprae may be misidentified because it is not represented in the current MicroScan or Vitek identification systems which are in use in many laboratories, but the organism can be differentiated by a few biochemical tests. S. caprae produces positive results for DNase, pyrrolidonyl aminopeptidase, and acid production from mannitol and maltose; it produces negative results for ornithine decarboxylase and tube coagulase.