The activities of antimicrobial combinations from three geographically diverse skin/tissue banks used in the processing of skin/ tissue were compared using bacteria and yeast isolated from burn patients. All formulations showed 90% or more effectiveness against bacteria generally susceptible to antibiotics but were less effective (60-80%) when tested against bacteria resistant to specific antimicrobials. Anti-yeast activity was present when an appropriate antifungal agent was included in the combination. All formulations were stable for at least six weeks. Results of this study raise certain questions about the use of these antimicrobial combinations in contemporary skin/tissue banking and point the way toward areas for future study.

Anti-Bacterial Agents↗

PubMed1997

Effect of thermal injury on the adherence of Candida albicans to murine splenic tissue.

In a mouse model of thermal injury, an increase in burn size produced a decrease in the ratio of Candida albicans cells adherent to the marginal zone to those adherent to the white pulp of the spleen, an increase in the number of Candida cells in the circulation and in the kidneys, and an increase in mortality.

Adhesiveness↗

PubMed1996

Recombinant neutral endopeptidase decreases oedema in the skin of burned guinea-pigs.

Oedema, due to increased vascular leakage postburn, cases significant problems for burn patients. The purpose of this study was to determine if local application of a recombinant neutral endopeptidase (rNEP) would reduce the increased vascular permeability caused by a burn. In a guinea-pig model, a single treatment of rNEP given immediately postburn significantly decreased burn-induced plasma extravasation. This rNEP effect was dependent upon both the dosage of the peptidase and its enzymatic activity. Additional experiments were consistent with the rNEP acting partly by degrading bradykinin, a mediator of increased vascular permeability postburn. These findings suggest that further study of rNEP as a possible treatment for oedema is warranted.

Analysis of Variance↗

PubMed1996

Circulating levels of tumour necrosis factor, interleukin 6 and proteolytic activity in a murine model of burn and infection.

Cytokines and proteinases have both been implicated as mediators in the inflammatory response associated with trauma and sepsis. Using a burned-infected mouse model, it was previously found that mortality is proportional to the amount of proteolytic activity (PA) in the circulation. However, little is known about circulating cytokine levels in hosts that are both burned and infected. With this mouse model, both tumour necrosis factor (TNF) and interleukin 6 (IL-6) were upregulated by a burn and by an infection. Burn plus infection produced an additive effect on each cytokine, but IL-6 levels correlated better with mortality. Treating mice with the proteinase inhibitor aprotinin immediately preburn and infectious challenge significantly decreased IL-6, PA and mortality. This may be a clinically relevant model for studying mediators in burned and/or septic hosts.

Animals↗

PubMed1996

Formulation of 'idealized' topical antimicrobial mixtures for use with cultured skin grafts.

In order to develop antimicrobial mixtures which provide broad-spectrum antimicrobial activity for use with cultured cell autografts, several individual antimicrobial agents, in concentrations non-toxic for cells in culture, were tested against a variety of bacteria and Candida spp. isolated from burn patients. An agar well diffusion topical assay was used. Antimicrobials active against Gram-positive and Gram-negative bacteria and antifungal agents, individually, were uniformly effective against their respective spectra of organisms. Broad-spectrum antibacterials were uniformly effective against Gram-negative bacteria but their activity varied against Gram-positive bacteria. Adding an agent active against Gram-positive bacteria to all broad spectrum antibacterial agents conferred uniform Gram-positive activity to the mixture. One mixture consisting of specific Gram-negative, Gram-positive and broad spectrum antibacterial agents, was uniformly active against all bacteria tested and the addition of antifungal agents extended the activity to cover Candida spp. without interfering with the mixture's overall antibacterial activity. Another mixture showed either additive or antagonistic activities against the battery of microorganisms tested. Thus, these methods can be used to identify mixtures of antimicrobials, in concentrations non-toxic for cells in culture, that have very broad spectra of antimicrobial activity. Such mixtures should be evaluated in patients when cultured skin grafts are used.

Administration, Topical↗

PubMed1996

Pyoverdin is essential for virulence of Pseudomonas aeruginosa.

The role of pyoverdin, the main siderophore in iron-gathering capacity produced by Pseudomonas aeruginosa, in bacterial growth in vivo is controversial, although iron is important for virulence. To determine the ability of pyoverdin to compete for iron with the human iron-binding protein transferrin, wild-type P. aeruginosa ATCC 15692 (PAO1 strain) and PAO pyoverdin-deficient mutants were grown at 37 degrees C in bicarbonate-containing succinate medium to which apotransferrin had been added. Growth of the pyoverdin-deficient mutants was fully inhibited compared with that of the wild type but was restored when pyoverdin was added to the medium. Moreover, when growth took place at a temperature at which no pyoverdin production occurred (43 degrees C), the wild-type PAO1 strain behaved the same as the pyoverdin-deficient mutants, with growth inhibited by apotransferrin in the presence of bicarbonate and restored by pyoverdin supplementation. Growth inhibition was never observed in bicarbonate-free succinate medium, whatever the strain and the temperature for growth. In vivo, in contrast to results obtained with the wild-type strain, pyoverdin-deficient mutants demonstrated no virulence when injected at 10(2) CFU into burned mice. However, virulence was restored when purified pyoverdin originating from the wild-type strain was supplemented during the infection. These results strongly suggest that pyoverdin competes directly with transferrin for iron and that it is an essential element for in vivo iron gathering and virulence expression in P. aeruginosa. Rapid removal of iron from [59Fe]ferritransferrin by pyoverdin in vitro supports this view.

Animals↗

PubMed1995

Studies on multiple Pseudomonas aeruginosa isolates from individual burn patients by RFLP, O antigen serotyping and antibiogram analysis.

Multiple isolates of Pseud. aeruginosa from individual burn patients were tested for antibiotic susceptibility-resistance patterns (antibiogram), O serotype lipopolysaccharide and chromosomal DNA restriction fragment length polymorphisms (RFLP) using a PAK pilin gene probe. Some patients were colonized by isolates identical by all three analytical procedures whereas other patients were found where multiple isolates were identical on the basis of serotype and antibiogram analysis, but different on the basis of RFLP analysis. Examples were found where multiple isolates from an individual patient appeared to be identical on the basis of serotyping and RFLP data, but different on the basis of antibiogram. Strains refractory to O serotyping could be characterized by RFLP type. These results indicate that RFLP analysis provides a valuable addition to routine serotyping and antibiogram studies on Pseud. aeruginosa isolates and that significant numbers of burn patients become co-colonized/co-infected with phenotypically diverse strains of this organism.

Burns↗

PubMed1995

Noncytotoxic combinations of topical antimicrobial agents for use with cultured skin substitutes.

Cultured skin grafts are destroyed more easily than split-thickness skin grafts by common burn wound organisms, including gram-negative and gram-positive bacteria and fungi. To increase the survival and engraftment of cultured skin grafts, formulations of antimicrobial agents were tested for cytotoxicity to cultured human keratinocytes and fibroblasts and for activity against common organisms from burn wounds. On the basis of previous studies, a base formulation containing neomycin (40 micrograms/ml), polymyxin B (700 U/ml), and mupirocin (40 micrograms/ml) was prepared, to which ciprofloxacin (20 micrograms/ml) or norfloxacin (20 micrograms/ml) and amphotericin B (0.25 microgram/ml) or nystatin (100 U/ml) were added. Toxicity to cultured human cells was determined by the growth response of cell cultures (n = 6) to each drug combination over 4 days. Activity against clinical isolates (n = 40) of Staphylococcus aureus, Pseudomonas aeruginosa, other gram-negative bacteria, and Candida spp. was determined by the wet disc assay. Analysis of variance testing showed no significant differences in the growth of keratinocytes or fibroblasts under control or experimental conditions. Medium without antimicrobial agents was not effective against any of the 40 microbial strains tested. The base formulation was effective against all bacterial strains tested but against none of the fungi, while all experimental formulations were effective against all microbial strains tested. These findings suggest that neomycin, mupirocin, and polymyxin B may be combined with a quinolone and an antimycotic agent to provide broad antimicrobial activity for a formulation for topical use with cultured skin on burns. However, the formulations described here are strictly experimental and are not recommended for clinical use without further evaluation.

Administration, Topical↗

PubMed1995

Avirulence of a Pseudomonas aeruginosa algC mutant in a burned-mouse model of infection.

The virulence of wild-type Pseudomonas aeruginosa PAO1 and that of a genetically defined algC mutant, PAO1 algC::tet, were compared in a burned-mouse model of infection. Unlike PAO1, PAO1 algC::tet was avirulent, grew less well in the eschar, and did not disseminate to the liver of challenged animals. We have previously shown that the P. aeruginosa algC gene is required for biosynthesis of alginate and lipopolysaccharide (M.J. Coyne, Jr., K.S. Russell, C.L. Coyle, and J.B. Goldberg, J. Bacteriol. 176:3500-3507, 1994). In order to determine whether the alginate or lipopolysaccharide (LPS) defect was responsible for the avirulence of this strain, we constructed a strain with a mutation in an alginate-specific gene, algD. PAO1-algD was virulent in the burned-mouse model, thus implicating the LPS defect in PAO1 algC::tet as the relevant alteration responsible for the avirulence of this strain.

Animals↗

PubMed1994

Agar well diffusion assay testing of bacterial susceptibility to various antimicrobials in concentrations non-toxic for human cells in culture.

Previously, we showed that microbial susceptibility to antimicrobials in concentrations non-toxic for human cells in culture could be tested using the wet disc topical antimicrobial assay. In this report, wet disc assay and agar well diffusion assay results were compared testing the susceptibility of Ps. aeruginosa isolates from burn patients to concentrations of Polymyxin B non-toxic for cultured cells. Both assays were performed on the same agar plates. No differences in results were observed. Further agar well diffusion assay testing showed that susceptibility/resistance could be demonstrated when testing several antimicrobials in concentrations non-toxic for cultured cells against a variety of bacteria isolated from burn patients. Therefore, the more familiar agar well diffusion as well as the wet disc assay can be used to test microbial susceptibility to these concentrations of antimicrobials.

Anti-Infective Agents↗

PubMed1994

Proteolytic activity and fatal gram-negative sepsis in burned mice: effect of exogenous proteinase inhibition.

Circulating proteolytic activity (PA) increases following burn or surgical trauma. Challenging traumatized mice with the yeast Candida albicans further increases PA. Once a PA threshold has been passed, mortality increases as PA increases. The purposes of this study were to determine (i) if gram-negative bacterial challenge affects circulating PA and mortality as Candida challenge does and (ii) if proteinase inhibitor treatment with aprotinin, antithrombin III, and alpha 1-proteinase inhibitor decreases circulating PA and increases the survival of burned mice infected with a bacterium. For all bacteria tested (Proteus mirabilis, Pseudomonas aeruginosa, and Klebsiella pneumoniae), burn plus challenge significantly elevated PA and mortality above levels in mice that were only burned or only challenged. Quantitative culture counts indicated that the mice died of sepsis. Proteinase inhibitor treatment of mice burned and challenged with K. pneumoniae significantly decreased circulating PA, decreased the hepatic microbial load, and increased survival. Hence, in traumatized mice challenged with either C. albicans or gram-negative bacteria, a relationship exists between proteolytic load and subsequent septic death. Parallels between these animal studies and human studies are discussed.

Animals↗

PubMed1993

Selection of topical antimicrobial agents for cultured skin for burns by combined assessment of cellular cytotoxicity and antimicrobial activity.

Cultured epidermal skin has become an adjunctive therapy for treatment of major burn injuries, but its effectiveness is greatly limited due to destruction by microbial contamination. To evaluate candidate drugs for use with cultured skin, a combined cytotoxicity-antimicrobial assay system was developed for determination of toxicity to cultured human keratinocytes and fibroblasts, and to common burn wound organisms (20 bacterial and 4 fungal strains). Candidate agents including Hibiclens (n = 3), amikacin, piperacillin, norfloxacin, and nystatin were tested separately and in combination (n = 6 each) for inhibition of growth of human cells and lytic activity on microorganisms in the wet disc assay. The data showed that: (1) Hibiclens was uniformly toxic to both cultured human cells and microorganisms; (2) norfloxacin had dose-dependent toxicity to human cells and broad effectiveness against microorganisms; and (3) norfloxacin (25 micrograms/mL) plus nystatin (100 U/mL) had low toxicity to human cells and high toxicity to both Gram-positive and Gram-negative bacteria (20 of 20) and fungi (4 of 4). Selection of topical antimicrobial drugs by these assays may improve effectiveness of cultured skin for burns and may be extended to the control of other surgical wound infections.

Administration, Topical↗

PubMed1993

Effect of a human IgG preparation rich in antibodies to a wide range of lipopolysaccharides on gram-negative bacterial sepsis in burned mice.

A human intravenous IgG preparation (Anti-LPS IgG) rich in antibodies to different lipopolysaccharides (LPS) and a normal human intravenous IgG (NIgG) were investigated for their ability to confer passive immunity. Both preparations were given at the time of infection (prophylaxis) or during sepsis (therapy) to burned mice with lethal infection induced by various clinically relevant gram-negative bacteria. When given at the time of infection both IgG preparations (5 mg/mouse) inhibited lethality induced by some bacteria (Pseudomonas aeruginosa serogroup G and B), but not others (Serratia marcescens, Klebsiella pneumonia, Proteus mirabilis), indicating a protection by by strain-specific antibodies. However, no significant protection was seen when mice were treated during sepsis. The range of specific antibody titers to the whole live bacteria and heat-killed (LPS-preserved) bacteria in the NIgG paralleled that of Anti-LPS IgG; however, the magnitude of the antibody titers did not accurately reflect the protective capacity in vivo. Thus, the exact specificity of the protective antibodies is still unknown. The protective effect of both IgG preparations was dose-dependent; at low IgG doses (0.5 mg/mouse) better protection was obtained with Anti-LPS IgG, whilst at higher doses (> or = 1 mg/mouse) both preparations exhibited identical effects. Low doses of either IgG preparation in combination with subtherapeutic doses of piperacillin significantly enhanced early survival (day 2 for NIgG and day 2 + 3 for Anti-LPS IgG) against P. aeruginosa, but the protective effect waned thereafter. We conclude that a strain-specific antibacterial effect in a compromised mouse infection model can be obtained by early passive immunization with human IgG from large plasma pools. It is suggested that Anti-LPS IgG or NIgG may be of benefit in some cases of gram-negative sepsis when administered as prophylaxis together with proper antibiotic treatment.

Animals↗

PubMed1993

Attachment of an aminoglycoside, amikacin, to implantable collagen for local delivery in wounds.

Cultured skin substitutes consisting of implantable collagen (COL) and cultured human skin cells often fail clinically from destruction by microbial contamination. Hypothetically, addition of selected antimicrobial drugs to the implant may control microbial contamination and increase healing of skin wounds with these materials. As a model for drug delivery, bovine skin COL (1 mg/ml) and amikacin (AM; 46 micrograms/ml) were modified by covalent addition of biotin (B-COL and B-AM, respectively) from B-N-hydroxysuccinimide and bound together noncovalently with avidin (A). B-COL was incubated with A and then with B-peroxidase (B-P) or by serial incubation with B-AM and B-P, before P-dependent chromogen formation. Colorimetric data (n = 12 per condition) from spot tests on nitrocellulose paper were collected by transmission spectrophotometry. Specificity of drug binding in spot tests was determined by (i) serial dilution of B-COL; (ii) reactions with COL, AM, or P that had no B; (iii) removal of A; or (iv) preincubation of B-COL-A with B before incubation with B-P. Binding of B-AM was (i) dependent on the concentration of B-COL; (ii) specific to B-COL, A, and B-P (P < 0.05); and (iii) not eluted by incubation in 0.15 or 1.0 M NaCl. B-AM was found to block binding of B-P to the B-COL-A complex and to retain bacteriocidal activity against 10 clinical isolates of wound bacteria in the wet disc assay. Antimicrobial activity of B-AM was removed from solution by treatment with magnetic A and a permanent magnet. These results suggest that selected antimicrobial drugs can be biotinylated for attachments to COL-cultured cell implants without loss of pharmacologic activity. Because this chemistry utilizes a common ligand, any molar ratio of agents may be administered simultaneously and localized to the site of implantation.

Amikacin↗