Effectiveness of a Glycylcycline Antibiotic for Reducing the Pathogenicity of Superantigen-Producing Methicillin-Resistant Staphylococcus aureus in Burn Wounds.

Objective: Burn-injured patients are highly susceptible to infectious complications, which are often associated with increased morbidity and mortality. Rates of antibiotic resistance have increased, and resistant species such as methicillin-resistant Staphylococcus aureus provide additional challenges in the form of virulence factors. Proteins can disrupt local healing, leading to systemic immune disruption. To optimize outcomes, treatments that reduce pathogenicity must be identified. This study aims to compare a glycylcycline antibiotic-tigecycline-with clindamycin for effectiveness in treating superantigenic methicillin-resistant Staphylococcus aureus in burn wounds. Methods: Sprague-Dawley rats received paired 2 × 2-cm burn wounds, which were subsequently inoculated with known virulence factor-producing methicillin-resistant Staphylococcus aureus or media alone on postinjury day 1. Infected animals received twice-daily tigecycline (high or low dose), twice-daily clindamycin (high or low dose), or saline alone (positive controls). Daily sampling and imaging assessments were performed. Results: Bacterial counts and toxin levels were reduced significantly in antibiotic-treated groups relative to positive controls (P < .001). Results from day 7 showed measurable toxin levels in clindamycin-treated, but not tigecycline-treated, wounds. Imaging analysis revealed a return of wound perfusion in tigecycline-treated animals similar to the sham animals. Transcript analysis using polymerase chain reaction and polymerase chain reaction arrays demonstrated downregulation of gene expression in antibiotic-treated animals as compared with positive controls. Conclusions: Overall, this study supports the use of tigecycline in the treatment of methicillin-resistant Staphylococcus aureus-infected burn wounds. While both protein synthesis inhibitors are effective, tigecycline appears to be superior in controlling toxin levels, enabling better wound healing.

Reduction of a multidrug-resistant pathogen and associated virulence factors in a burn wound infection model: further understanding of the effectiveness of a hydroconductive dressing.

OBJECTIVE: Drawtex's ability to remove pathogens and associated virulence factors has been demonstrated in vitro. A model of burn wound infection was used to characterize the in vivo impact of this dressing on infection and wound healing. METHODS: Paired burn wounds were created on the dorsum of Sprague Dawley rats and were inoculated with methicillin-resistant Staphylococcus aureus (MRSA). Animals were divided into 2 groups, half with wounds that received experimental dressing and the remaining half with control dressing-treated wounds. Dressings remained in place through 3, 6, 9, or 14 days after injury, and methicillin-resistant S aureus and virulence factors were quantified. Laser Doppler imaging was used to examine wound perfusion, and local host immune response was assessed through the quantification of mRNA expression. RESULTS: By day 3, less methicillin-resistant S aureus was measured in wounds treated with experimental-dressing compared to control-dressing wounds. Quantities remained lower in the experimental group through day 14 (P < .001). More methicillin-resistant S aureus was quantified in the experimental dressing itself than in control dressing at all time points (P < .05). Experimental dressing-treated wounds contained less toxic shock syndrome toxin 1 and Panton-Valentine leukocidin than controls (P < .01) on days 6, 9, and 14. Induction of toll-like receptor 2, NOD-like receptor family, pyrin domain containing 3, and interleukin 6 was significantly lower in experimental-dressing treated wounds than in controls on days 6 and 9 (P < .05). CONCLUSIONS: The hydroconductive dressing provided a significant reduction in pathogen and virulence factors compared to a control dressing. As a result of clearance of virulence factors from the wound bed, a requisite alteration in host innate immune response was observed.

Regional neurovascular inflammation and apoptosis are detected after electrical contact injury.

High-voltage electrical injuries are a devastating form of trauma often treated in burn centers. Examining superficial wounds alone may lead to an inaccurate assessment of local, regional, and systemic severity of injury. In this work, the neurovasculature at sites regionally distinct from the contact wound were assessed for cellular pathology. Nine male Sprague-Dawley rats subjected to 1000 V direct-current shocks were separated into three groups: high-shock (>10-second contact), low-shock (<4-second contact), and control. Injury video was captured with a forward-looking infrared camera, and a thermal excitation analysis was performed. The neurovascular bundles from the iliofemoral region to the distal posterior tibial region were dissected from the hind limbs of the shocked animals and stained by immunohistochemistry for antibodies specific to apoptosis (APO) 1, caspase-3, activating transcription factor 3, high-mobility group box-1, granulocyte-macrophage colony-stimulating factor and interleukin-6. Real-time reverse-transcription polymerase chain reaction was used to quantify differential transcript levels of superoxide dismutases 1, 2, and 3 and heat-shock protein 70 from peripheral blood mononuclear cells and liver tissue. Finally, a protein array was used to identify key inflammatory cytokines in blood plasma. Significant dose-dependent trends were identified in apoptotic markers as well as inflammatory markers in both arterial and nerve tissues. Although arterial tissue exhibited a gradual decline in these markers proximally from the wound site, nerve tissue maintained a constant level at every location. Transcript analysis revealed an up-regulation of extracellular superoxide dismutase, and down-regulation of heat-shock protein 70, whereas plasma inflammatory cytokine levels indicated no significant changes. Thermal excitation analysis revealed a linear temperature increase, with a dose-dependent thermal maximum. In this study the authors have shown that neurovascular APO and inflammation are present at locations extremely proximal to electrical injury contact sites and this appears to be dose-dependent. Nerve tissue APO and inflammation may extend farther proximally than the iliofemoral region, and multiple proapoptotic mechanisms may be activated. No systemic inflammatory response was indicated in this study.

Treatment with an oxazolidinone antibiotic inhibits toxic shock syndrome toxin-1 production in MRSA-infected burn wounds.

Mortality rates in burn patients increase if they experience complications of infection. Frequently, the organisms associated with such infections are Staphylococci, including antibiotic-resistant species such as methicillin-resistant Staphylococcus aureus. Virulence factor production can further complicate treatment as a localized toxin presence may derail the healing process and allow a more invasive infection, while a toxin that becomes systemic can induce shock and cause host immune disruption. Male rats were anesthetized and subjected to full-thickness burn wounds. One day postinjury, wounds were inoculated with Toxic Shock Syndrome Toxin-1-producing methicillin-resistant S. aureus. Animals were then divided into three treatment groups: vancomycin, linezolid, or positive control. For nine additional days, animals received twice-daily antibiotics and wound assessments, blood draws, and wound biopsies were performed. All animals had wound quantitative cultures that exceeded 1 × 10 colony forming units (CFU) per gram 1 day after inoculation. Linezolid treatment significantly reduced the bacterial counts in the wounds. Positive controls and vancomycin-treated animals had toxins in their wounds by day 5 and this remained throughout the study (ranging from 20-80 ng/ml). Linezolid-treated animals had significant decrease in toxin production (< 5 ng/ml), and in most cases toxins were undetectable. No animals became systemically infected with bacteria at any point during the study. Superantigen production in burn wounds has morbid consequences in terms of long-term wound healing. A S. aureus burn wound infection model was created that allowed the study of the effect of two standard-use antibiotics on local burn wound pathophysiology. Most noteworthy is that low-dose linezolid arrested toxin production in the wound.

Novel application of a spatial frequency domain imaging system to determine signature spectral differences between infected and noninfected burn wounds.

Complications of infection can increase burn-related morbidity and mortality. Early detection of burn wound infection could lead to more precise and effective treatment, reducing systemic complications and the need for long-term, broad-spectrum intravenous antibiotics. Quantitative cultures from biopsies are the accepted standard to determine infection. However, this methodology can take days to yield results and is invasive. This investigation focuses on the use of noninvasive imaging to determine the infection status of burn wounds in a controlled in vivo model. Full-thickness burn wounds were created on the dorsum of adult male rats (n = 6). Twenty-four hours after burn wound creation, wounds in the "Infected" group were inoculated with a vehicle containing 1 × 10(8) colony forming unit Staphylococcus aureus. "Control" group animals received vehicle alone. Subsequently, the wounds were imaged daily for a total of 10 days and the differences of skin optical properties were assessed using spatial frequency domain imaging at 16 different wavelengths from 500 to 700 nm. Regions of interest on the resulting images were selected and averaged at each time point. Statistically significant differences in average absorption and reduced scattering coefficients (µ(a) and µ(s)') at 620 and 700 nm were observed between the two groups (P < .05). Differential optical properties were most evident by day 4 and persisted throughout the time course. Differential signature changes in optical properties are evident in infected burn wounds. This novel application of spatial frequency domain imaging may prove to be a valuable adjunct to burn wound assessment. Further work will be aimed at determining dose-response relationships and prokaryotic species differences.

Localization of superantigen virulence factors in kidney tissue of animals with Staphylococcus aureus-infected burn wounds.

Gram-positive organisms are often found in association with burn wounds. A paucity of information exists regarding the accumulation and fate of virulence factors from these bacteria. The superantigenic exotoxins produced by Staphylococcus aureus are potent immunomodulating proteins and have also been described to localize in the kidney. The aim of this work was to demonstrate renal accumulation of toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxin B (SEB) in a methicillin-resistant S. aureus burn wound infection. Twelve Sprague Dawley rats were subjected to partial-thickness burns (2 × 2 cm) using an aluminum billet. On postburn day 1, the wounds were inoculated with a toxin-producing strain of methicillin-resistant Skin biopsies and serum were obtained on postburn days 3, 6, and 10 along with necropsies for three animals each day. An enzyme-linked immunosorbent assay was used to quantify amounts of TSST-1 and SEB. Immunohistochemistry was used to localize SEB, TSST-1, and cleaved caspase-3 in renal tissue, and quantitative real-time polymerase chain reaction was used to assess erythropoietin and endothelin-1 messenger RNA (mRNA) in renal tissue. Baseline skin and plasma levels of TSST-1 and SEB were not detectable. Skin biopsy TSST-1 levels were detected on all postburn days and peaked at a mean value of 39.35 ng/ml on day 6; SEB was found in the skin and kidney only on postburn days 6 and 10. An enzyme-linked immunosorbent assay of renal tissue for TSST-1 and SEB demonstrated significantly higher (P < .05) mean toxin concentrations on postburn day 10: 10.87 ng/ml for TSST-1 and 0.67 ng/ml for SEB. Immunohistochemistry of renal tissue demonstrated increased stain intensity for SEB, TSST-1, and cleaved caspase-3 over time. Quantitative real-time polymerase chain reaction demonstrated decreased expression erythropoietin mRNA and increased expression of endothelin-1 mRNA relative to negative controls (P < .01). In a burn wound infection model that is nonlethal and lacks bacteremia, TSST-1 and SEB traverse cutaneous wounds and localize to the kidney. These potent virulence factors may contribute to the induction of apoptosis, and may alter homeostasis via renal pathophysiology.