Antibiotic susceptibility and resistance of Staphylococcus aureus isolated from fresh porcine skin xenografts: risk to recipients with thermal injury

The previous use of fresh porcine xenografts at the Prague Burn Centre had raised concerns over the transmission of zoonotic pathogens. This study examines the risk of zoonotic Staphylococcus aureus colonisation of burn patients from fresh porcine skin xenografts. Samples were collected from the nares, skin and perineum of commercial pigs (n=101) and were screened for methicillin sensitive S. aureus (MSSA) and resistant S. aureus (MRSA). The efficacy of the antibiotic wash used in decontamination of the pigskin was tested against planktonic- and biofilm-grown isolates. The spa type of each isolate was also confirmed. All pig swabs were negative for MRSA but 86% positive for MSSA. All planktonic-grown isolates of MSSA were sensitive to chloramphenicol and nitrofurantoin and 44% of isolates were resistant to streptomycin. Isolates grown as biofilm exhibited higher rates of antimicrobial resistance. Sequence analysis revealed three distinct spa types of the MRSA ST398 clonal type. This finding demonstrates the existence of a MSSA reservoir containing spa types resembling those of well-known MRSA strains. These MSSA exhibit resistance to antibiotics used for decontamination of the pigskin prior to xenograft. Amended use of procurement could allow the use of fresh pigskin xenografts to be reinstated.

Polymeric multilayers that localize the release of chlorhexidine from biologic wound dressings

Biologic wound dressings contain animal-derived components and are susceptible to high infection rates. To address this issue, we report an approach that permits incorporation of non-toxic levels of the small molecule antiseptic 'chlorhexidine' into biologic dressings. The approach relies on the fabrication of polyelectrolyte multilayer (PEMs) films containing poly(allylaminehydrochloride) (PAH), poly(acrylicacid) (PAA), and chlorhexidine acetate (CX) on elastomeric poly(dimethylsiloxane) (PDMS) sheets. The PEMs (20-100 nm thick) are subsequently stamped onto the wound-contact surface of a synthetic biologic dressing, Biobrane, which contains collagen peptides. Chlorhexidine loading in the PEMs was tailored by tuning the number of (CX/PAA) bilayers deposited, providing burst release of up to 0.98 ± 0.06 μg/cm(2) of CX over 24 h, followed by zero-order release of 0.35 ± 0.04 μg/cm(2)/day for another week. Although the CX concentrations released were below the reported in vitro cytotoxicity limit (5 μg/mL over 24 h) for human dermal fibroblasts, they killed 4 log(10) counts of pathogenic bacteria Staphylococcus aureus in solution. The CX/PEMs could be stamped onto Biobrane with high efficiency to provide CX release kinetics and in vitro antibacterial activity similar to that on PDMS stamps. In a full-thickness 'splinted' dermal wound-model in normal wild-type mice, the CX-functionalized Biobrane showed no decrease in either its adherence to the wound-bed or wound closure rate over 14 days. The murine wounds topically inoculated with ∼10(5) CFU/cm(2) of S. aureus and treated with CX-functionalized Biobrane demonstrated a 3 log(10) decrease in the wound's bacterial burden within 3 days, compared to persistent bacterial colonization found in wounds treated with unmodified Biobrane (n = 10 mice, p < 0.005). Overall, this study presents a promising approach to prevent bacterial colonization in wounds under biologic dressings.

Microbiological safety and clinical efficacy of radiation sterilized amniotic membranes for treatment of second-degree burns

Amniotic membranes collected from the placentae of screened donors were processed and sterilized by gamma irradiation at 25 kGy. The sterility assurance level (SAL) of gamma irradiated amniotic membranes and clinical efficacy in second-degree burn wound healing were evaluated. Processed air-dried amniotic tissue from 159 batches of processing was checked for the bioburden level before sterilization. About 39% of the tissues had bioburden in the range of 10(1)-10(2)/100 cm(2) and 54.8% in the range of 10(2)-10(3)/100 cm(2). Based on the bioburden of the processed tissue prior to sterilization and the D(10) value of 2.3 kGy for the radiation resistant reference strain Bacillus pumilus, the sterility assurance level of the amniotic membranes irradiated at 25 kGy is found to be 10(-7) to 10(-11). The burn wound healing rate was compared between the radiation sterilized amniotic membranes and glycerol preserved amniotic membranes. Fifty patients with partial-thickness burns (up to 70% TBSA) were selected for the study. The scalds constituted 82% (41 patients) whereas flame burns accounted for 18% (9 patients). Various aspects like ease of application, patient comfort, development of fluid under the membrane, bacterial culture of drained fluid, rate of epithelialization, development of hypertrophic scars, keloids, unstable scars and restriction of joint movements were recorded with the application of gamma irradiated and glycerol preserved membranes. Radiation sterilized amniotic membranes had advantage over the glycerolized membranes with respect to the ease of application. Five patients with glycerol preserved membranes and four with gamma irradiated membranes developed fluid. The bacteriology of fluid showed Pseudomonas aeruginosa in four cases, Staphylococcus aureus in two cases, Escherichia coli in two cases and Acinetobacter in one case. The application of radiation sterilized amniotic membranes on the burn wound favoured epithelialization. In all the patients, membranes dessicated and separated in 10-14 days time leaving behind an epithelialized surface.

Microbial keratitis after amniotic membrane transplantation

PURPOSE

To determine the incidence of early-onset (<30 days) and late-onset (>30 days) microbial keratitis after treatment of persistent corneal epithelial defects with amniotic membrane transplantation (AMT) utilizing tissue acquired from a commercial laboratory or prepared by the institutional eye bank.

METHODS

A retrospective, non-randomized, sequential, comparative study was performed for every patient with a persistent corneal epithelial defect who underwent primary AMT at KKESH between January 1, 2003 and June 30, 2004.

RESULTS

A total of 142 AMT procedures were performed for persistent corneal epithelial defects during the study period. There were 72 cases using commercially prepared tissue and 70 cases using locally prepared tissue. The mean patient age was 50.3+/-25.6 years (range, 1-104 years). The mean follow up was 6.3+/-5.0 months (range, 1-21 months). There were no cases of early-onset microbial keratitis in cases in which either commercially acquired tissue or locally prepared tissue was used.

CONCLUSION

Amniotic tissue prepared in a commercial laboratory or by properly qualified eye bank personnel may be used for AMT in eyes with persistent corneal epithelial defects with minimal risk of microbial keratitis in the first postoperative month.

[Biophysical properties of membrane dressing made of bacterial cellulose]

In the paper, review of papers devoted to biophysical properties of membrane dressing made of bacterial cellulose was done. These properties were determined on the basis of studies on osmotic and diffusive transport through pure (non modified) bacterial cellulose membrane form called Bio-Fill. The measures of these properties are values of membrane transport parameters resulted from Kedem-Katchalsky's theory and interferograms of near-membrane regions made laser interferometric method.

[Medical properties of the membrane dressing made of bacterial cellulose]

Review of papers devoted to medical properties of membrane dressing made of bacterial cellulose was done. These properties were determined on the basis of studies on application of this membrane to venous leg ulcer healing. Moreover, quantitative method of valuation of wound healing process efficiency which lies in calculating efficiency coefficient was described. Value of this coefficient is directly proportional to ulcer healing speed and indirectly proportional to product of initial surface and healing time.