Early detection of bone infection and differentiation from post-surgical inflammation using 2-deoxy-2-[18F]-fluoro-D-glucose positron emission tomography (FDG-PET) in an animal model.

Diagnosing bone infection in the context of post-surgical inflammation is problematic since many of the early signs of infection are similar to normal post-surgical changes. We used a rabbit osteomyelitis model to evaluate the use of 2-deoxy-2-[(18)F]-fluoro-d-glucose positron emission tomography (FDG-PET) as a means of detecting post-operative infection in the context of post-surgical inflammation. Comparisons were made between infected and non-infected rabbits in which infection with Staphylococcus aureus was initiated at the time of surgery. Weekly PET scans were obtained 30 and 60 min after the introduction of FDG and analyzed based on standardized uptake values (SUV) at the surgical site and visual assessment of the presence or absence of infection. Concurrent X-rays were taken immediately prior to scanning. At 4weeks post-operatively, animals were sacrificed for histologic and bacteriologic confirmation of infection. Uptake of FDG was evident in the bone of all rabbits on day 1 post-surgery, however, SUV comparisons from the surgical site could not be used to distinguish between the infected and uninfected groups until day 15. Visual analysis of FDG-PET scans revealed a significant difference (p<0.01) between the infected and uninfected groups as early as day 8. This was due in part to the ability to visualize regional lymph nodes by FDG-PET.

The treatment of experimental osteomyelitis by surgical debridement and the implantation of calcium sulfate tobramycin pellets.

Calcium sulfate was used as a biodegradable delivery system for the administration of antibiotics in musculoskeletal infection. New Zealand white rabbits were infected with Staplylococcus aureus, debrided, and randomized to one of four treatment groups: calcium sulfate pellets with 10% tobramycin sulfate, placebo calcium sulfate pellets and IM tobramycin, placebo calcium sulfate pellets, or debridement. Serum and wound exudate tobramycin concentrations and serum calcium levels were measured. Radiographs, cultures, and histology were analyzed for efficacy and treatment. Rabbits treated with 10% tobramycin sulfate pellets showed a significantly higher eradication of infection (11/13) than rabbits treated with debridement only (5/12), placebo pellets and IM tobramycin (5/14). or placebo pellets (3/13). In the group receiving 10% tobramycin sulfate pellets, serum tobramycin concentrations peaked 3 h post-operatively at 5.87 microg/ml and were non-detectable after day 1. In the group receiving placebo pellets and IM tobramycin, serum concentrations peaked at 7.82 microg/ml 1 h post-operatively, fell to 6.12 microg/ml on day 2, and averaged 4.18 microg/ ml for the remainder of the treatment period. The wound exudate tobramycin concentrations in the animals treated with tobramycin sulfate pellets peaked at 11.9 mg/ml on day 1 and dropped to 2.5 microg/ml on day 7. There was no significant difference in the serum calcium levels in any of the treatment groups. Calcium sulfate containing tobramycin sulfate has potential utility as a biodegradable local antibiotic delivery system in the treatment of musculoskeletal infections.

Protein gene product 9.5 (PGP 9.5) is not a specific marker of neural and nerve sheath tumors: an immunohistochemical study of 95 mesenchymal neoplasms.

In non-neoplastic tissues, the expression of protein gene product 9.5 (PGP 9.5), a member of the ubiquitin hydrolase family of proteins, is confined to neural and neuroendocrine cells. Although it has been claimed that PGP 9.5 is a specific marker of neural and/or nerve sheath differentiation in human tumors, careful review of the literature suggests that relatively few nonneural or nerve sheath tumors have been studied. Prompted by our recent observation of a PGP 9.5-positive malignant fibrous histiocytoma, we undertook a study of PGP 9.5 expression in a large group of well-characterized mesenchymal neoplasms. Sections from 95 mesenchymal tumors were retrieved from our archives and immunostained for PGP 9.5 using standard avidin-biotin complex technique and heat-induced epitope retrieval. Scoring was as follows: negative, 1+ (<10-25% of cells), 2+ (25-50% of cells), and 3+ (>50% of cells). Normal nerves and fibrous tissue were internal positive and negative controls, respectively. Positive immunostaining was seen in 80/95 (84%) of cases. Positive results by tumor subtype were as follows: (1) nerve sheath tumors: malignant peripheral nerve sheath tumor (7/10), neurofibromas (10/10), and perineuriomas (3/3); (2) (Myo) fibroblastic tumors: malignant fibrous histiocytoma (18/20), low-grade fibromyxoid sarcomas (8/9), fibromatoses (7/7), and desmoplastic fibroblastomas (2/2); (3) vascular tumors: angiosarcomas (4/4), hemangioendotheliomas (3/5), and hemangiomas (3/4); and (4) other non-nerve sheath tumors: pleomorphic liposarcoma (4/4), dermatofibrosarcoma protuberans (2/5), rhabdomyosarcomas (2/2), synovial sarcomas (8/8), melanomas (1/2). All positive cases were 2-3+ except 6 malignant peripheral nerve sheath tumor, 1 neurofibroma, 3 malignant fibrous histiocytoma, 2 low-grade fibromyxoid sarcoma, and 1 dermatofibrosarcoma protuberans. Positive staining was seen in normal smooth muscle and germinal centers in addition to nerves. We conclude that in this, the largest study to date of PGP 9.5 expression in mesenchymal neoplasms, we have found strong (2-3+) expression in the vast majority of nonneural or nerve sheath neoplasms studied. Although PGP 9.5 is a sensitive neural/nerve sheath marker, it is essentially totally nonspecific for diagnostic purposes. It is possible that our findings reflect cross-reactivity of the 13C4 clone with epitopes present on other ubiquitin hydrolases. Alternatively, PGP 9.5 expression may be aberrantly up-regulated in a variety of mesenchymal neoplasms.

Role of sarA in the pathogenesis of Staphylococcus aureus musculoskeletal infection.

We recently demonstrated that mutation of sarA in clinical isolates of Staphylococcus aureus results in a phenotype that is distinct by comparison to sarA mutants generated in the laboratory strain RN6390 (J. S. Blevins, K. E. Beenken, M. O. Elasri, B. K. Hurlburt, and M. S. Smeltzer, Infect. Immun. 70:470-480, 2002). This raises the possibility that studies demonstrating that RN6390 sarA mutants are attenuated do not accurately reflect the role of sarA in the pathogenesis of staphylococcal disease. To test this hypothesis, we used a murine model of musculoskeletal infection to assess the virulence of sarA and agr mutants generated in a clinical isolate of S. aureus (UAMS-1). By using this model, we confirmed that mutation of sarA and/or agr results in a reduced capacity to cause both septic arthritis and osteomyelitis.