Broth versus solid agar culture of swab samples of cadaveric allograft musculoskeletal tissue

Positive "Surprise" Broth Cultures in Nonunion Surgery Do Not Require Antibiotic Treatment

The objective of this study was to review the efficacy of a treatment approach for patients with positive intraoperative cultures during fracture nonunion surgery. The authors performed a retrospective case series at a level I trauma center. In this series, 60 patients without preoperative concern for infection were surgically treated for fracture nonunion. The treatment course of patients after fracture nonunion surgery, including culture results, antibiotic administration, and the presence of clinical infection and radiographic union, was studied. Sixty patients underwent fracture nonunion surgery. Twenty-four patients had a positive intraoperative culture. Fourteen patients had only a positive broth culture, 6 had only a positive routine culture, and 4 had positive mixed (routine and broth) cultures. The most common bacteria was coagulase-negative staphylococci, isolated in 19 of 24 patients, and the only isolated organism in 13 of 24 patients. Patients with a positive broth culture were not treated with antibiotics. Four of 10 patients with either a positive routine or mixed culture grown within 3 days of surgery were treated with antibiotics. All patients achieved clinical healing without signs of infection, and all but 2 patients achieved radiographic union at a mean follow-up of approximately 5 years. In the setting of fracture nonunion surgery, patients with only a positive broth culture and those with only a positive routine or mixed cultures that grew in a delayed fashion (>3 days postoperatively) did not require antibiotic treatment to achieve healing. [Orthopedics. 2019; 42(6):e532-e538.].

An allograft generated from adult stem cells and their secreted products efficiently fuses vertebrae in immunocompromised athymic rats and inhibits local immune responses

BACKGROUND CONTEXT

Spine pain and the disability associated with it are epidemic in the United States. According to the National Center for Health Statistics, more than 650,000 spinal fusion surgeries are performed annually in the United States, and yet there is a failure rate of 15%-40% when standard methods employing current commercial bone substitutes are used. Autologous bone graft is the gold standard in terms of fusion success, but the morbidity associated with the procedure and the limitations in the availability of sufficient material have limited its use in the majority of cases. A freely available and immunologically compatible bone mimetic with the properties of live tissue is likely to substantially improve the outcome of spine fusion procedures without the disadvantages of autologous bone graft.

PURPOSE

This study aimed to compare a live human bone tissue analog with autologous bone grafting in an immunocompromised rat model of posterolateral fusion.

DESIGN/SETTING

This is an in vitro and in vivo preclinical study of a novel human stem cell-derived construct for efficacy in posterolateral lumbar spine fusion.

METHODS

Osteogenically enhanced human mesenchymal stem cells (OEhMSCs) were generated by exposure to conditions that activate the early stages of osteogenesis. Immunologic characteristics of OEhMSCs were evaluated in vitro. The secreted extracellular matrix from OEhMSCs was deposited on a clinical-grade gelatin sponge, resulting in bioconditioned gelatin sponge (BGS). Bioconditioned gelatin sponge was used alone, with live OEhMSCs (BGS+OEhMSCs), or with whole human bone marrow (BGS+hBM). Efficacy for spine fusion was determined by an institutionally approved animal model using 53 nude rats.

RESULTS

Bioconditioned gelatin sponge with live OEhMSCs did not cause cytotoxicity when incubated with immunologically mismatched lymphocytes, and OEhMSCs inhibited lymphocyte expansion in mixed lymphocyte assays. Bioconditioned gelatin sponge with live OEhMSC and BGS+hBM constructs induced profound bone growth at fusion sites in vivo, with a comparable rate of fusion with syngeneic bone graft (negative [0 of 10], BGS alone [0 of 10], bone graft [7 of 10], BGS+OEhMSC [10 of 15], and BGS+hBM [8 of 8]).

CONCLUSIONS

Collectively, these studies demonstrate that BGS+OEhMSC constructs possess low immunogenicity and drive vertebral fusion with efficiency matching syngeneic bone graft in rodents. We also demonstrate that BGS serves as a promising scaffold for spine fusion when combined with hBM.

The visual assessment of broth cultures for tissue bank samples

The bioburden screening process of allograft musculoskeletal tissue samples received at the South Eastern Area Laboratory Services includes the routine use of solid agar and cooked meat (CM) broth media. CM has been routinely sub-cultured onto solid agar plates after aerobic incubation at 35 °C. This study will evaluate whether a visual assessment of CM can replace sub-culture by an in vitro inoculation and a prospective study. Eight challenge organisms were serially diluted and inoculated into CM. The average inoculum of 0.5-5.5 CFU produced visible turbidity of CM after 24-h incubation for 7 of the challenge organisms with one organism producing turbidity after 48-h incubation. The prospective study evaluated 222 CM of which 213 were visually clear and no-growth on sub-culture and 9 turbid CM which were culture positive. Broth cultures are an integral part of the bioburden screening process of allograft musculoskeletal tissue and swab samples and visual assessment of CM can replace sub-culture.

Improved microbiological diagnostic due to utilization of a high-throughput homogenizer for routine tissue processing

Tissue specimens are valuable materials for microbiological diagnostics and require swift and accurate processing. Established processing methods are complex, labor intensive, hardly if at all standardizable, and prone to incorporate contaminants. To improve analyses from tissue samples in routine microbiological diagnostics, by facilitating, fastening, and standardizing processing as well as increasing the microbial yield, performance of Precellys 24 high-throughput tissue homogenizer was evaluated. Therefore, tissue samples were artificially inoculated with Staphylococcus aureus, Escherichia coli, and Candida albicans in 3 different ways on the surface and within the material. Microbial yield from homogenized samples was compared to direct plating method. Further, as proof of principle, routine tissue samples from knee and hip endoprosthesis infections were analyzed. The process of tissue homogenization with Precellys 24 homogenizer is easy and fast to perform and allows for a high degree of standardization. Microbial yield after homogenization was significantly higher as compared to conventional plating technique.

Swab or biopsy samples for bioburden testing of allograft musculoskeletal tissue?

Swab and biopsy samples of allograft musculoskeletal tissue are most commonly collected by tissue banks for bacterial and fungal bioburden testing. An in vitro study was performed using the National Committee for Clinical Laboratory Standards standard 'Quality control of microbiological transport systems' (2003) to validate and evaluate the recovery of six challenge organisms from swab and biopsy samples of allograft musculoskeletal tissue. On average, 8.4 to >100 and 7.2 to >100 % of the inoculum was recovered from swab and biopsy samples respectively. A retrospective review of donor episodes was also performed, consisting of paired swab and biopsy samples received in this laboratory during the period 2001-2012. Samples of allograft femoral heads were collected from living donors during hip operations. From the 3,859 donor episodes received, 21 paired swab and biopsy samples each recovered an isolate, 247 swab samples only and 79 biopsy samples only were culture positive. Low numbers of challenge organisms were recovered from inoculated swab and biopsy samples in the in vitro study and validated their use for bioburden testing of allograft musculoskeletal tissue. Skin commensals were the most common group of organisms isolated during a 12-year retrospective review of paired swab and biopsy samples from living donor allograft femoral heads. Paired swab and biopsy samples are a suitable representative sample of allograft musculoskeletal tissue for bioburden testing.