The Effect of an Antimicrobial Gauze Dressing Impregnated with 0.2-Percent Polyhexamethylene Biguanide as a Barrier to Prevent P

Introduction Gauze-type dressings are designed to absorb fluid, protect the wound from the outside environment, and protect the outside environment from wound fluids. Many types of wound dressings have become commercially available over the past several years. Some of these dressings are known to provide physical protection for wounds;[1] however, few have been designed specifically to protect against invasion of external microorganisms with the potential to reduce the possibility of infection. The purpose of this study was to examine the protective barrier activity of a gauze dressing containing an antimicrobial agent. The surface of the dressing covering partial-thickness wounds was challenged with a suspension of Pseudomonas aeruginosa (P. aeruginosa) bacteria in normal saline. P. aeruginosa, an aerobic, nonspore-forming, gram-negative rod, continues to be one of the most important pathogens associated with infections and patients’ morbidity and mortality.[2] This organism has great adaptability to a variety of moist environments, and its virulence spectrum ranges from superficial skin infections to fulminate sepsis. Additionally, P. aeruginosa produces a water-soluble pigment, pyoverdin, which fluoresces in long-wave UV black light (320–400nm), which is observable when P. aeruginosa organisms are present. This visual fluorescent pigment can be highly reliable for the detection of P. aeruginosa in an environment. Polyhexamethylene biguanide (PHMB) (Avecia, Inc., Wilmington, Delaware) is a heterodisperse mixture of polymers, and its activity as an antimicrobial agent is well accepted.[3–5] It was selected as the antimicrobial agent to be added to a commercially available gauze dressing.* PHMB’s basic unit can be repeated from 2 to 30 times with increasing chain length correlating with increasing antimicrobial efficacy. End groups (specifically aminohydrochloride group or a cyanoguanidine or guanidine group) also contribute to activity, but less so as molecular weight increases. Lethal action of PHMB concerns interaction at the cytoplasmic membrane to cause nonspecific alterations in membrane permeability. There is a specific association of PHMB with the acidic lipid components of the membrane to cause phase separation and domain formation. Increased size of the polymer increases the magnitude of the membrane perturbation. Materials and Methods Experimental animals. Three young specific-pathogen free (SPF) pigs (Ken-O-Kaw Farms, Windsor, Illinois) weighing 40 to 50kg were used. A porcine model was chosen because of the morphological and functional similarity of pig skin to human skin[6,7] and because the type of microflora normally present is similar to human skin.[8] The animals were conditioned for two weeks prior to initiating the experimental studies. The animals were fed a nonantibiotic chow ad libitum and housed in our facilities (meeting U.S. Department of Agriculture compliance) with controlled temperatures (19–21 degrees C) and controlled light and dark cycles (12 hours light and 12 hours dark). The University of Miami Animal Care Committee approved the animal protocols used in these studies, and all procedures followed were in compliance with the federal guidelines for the care and use of laboratory animals (NIH Publication No. 86-23, Revised 1985). This study was conducted in compliance with the University of Miami’s Department of Dermatology and Cutaneous Surgery’s Standard Operating Procedures (SOPs). In order to help minimize possible discomfort, an analgesic patch (fentanyl transdermal system, 25mg/hr) was used on each animal during the entire study. Wounding technique. Animals were pre-anesthetized with ketamine HCL (20mg/kg), atropine (0.5 mg/Kg), and xylazine (0.5mg/kg) IM, followed by mask inhalation of an isoflurane and oxygen combination. Buprenex 0.1mg/kg was administered IM on the first day only. For pain management, fentanyl transdermal system patches (25mg/hr) were applied to the animals and replaced every three days. The skin on the back and both sides of the animals was clipped with standard animal clippers and prepared for wounding by washing with a nonantibiotic soap and sterile water. Partial-thickness rectangular wounds (7mm x 10mm x 0.3mm) were made using a modified electrokeratotome (Storz, St. Louis, Missouri).[9] Hemostasis was achieved using sterile surgical gauze. Study Design Microbial barrier. Three animals were used for this study. Eighteen wounds were made in two groups of nine wounds each. The wounds were separated by at least 5cm of normal unwounded skin. Nine wounds were assigned to one of the following groups: 1) the antimicrobial-impregnated gauze dressing with 0.2-percent PHMB* or 2) gauze without the biocidal agent, controlCazzanigaFig1LG.jpgsubendsubCazzinigaFig_2tif.jpgCazzinigaFig_3tif.jpgCazzanigaTable1LG.jpgCazzanigaTable2LG.jpgCazzinigaFig_4tif.jpgCazzinigaFig_5tif.jpgsubendsub** The PHMB dressing was examined for its ability to act as a barrier to invasion by P. aeruginosa organisms in experimentally induced wounds. Controls for these studies included a gauze dressing without an antimicrobial. A reduction in the number of P. aeruginosa able to gain entry into the wound with the PHMB dressing when compared with the control dressing was observed. This was shown at all assessment times and suggests that the addition of PHMB to the gauze dressing is preventing P. aeruginosa from penetrating the dressing and/or surviving once reaching the wound. The ability of gauze dressing to prevent the entrance of pathogenic bacteria may have important clinical implications that could result in decreased rates of infection in natural wounds. In order to be confident in this assessment, further studies, particularly in natural wounds of patients, should be performed. Our studies suggest that this dressing will be efficacious in this setting. The effect of this antimicrobial-impregnated dressing on normal flora is another important topic addressed in this study. Culture of normal epidermal flora was also performed as reported in Table 2 and Figure 5 of the Results section. There was no consistent difference between the number of normal flora isolated from the antimicrobial and control dressings. This is relevant, since native skin flora is vital to the health of the epidermis and is believed to play a role in preventing proliferation of pathogens. Further studies should be conducted to determine the effect of the PHMB dressing on pathogenic organisms other than P. aeruginosa. Studies have already been conducted showing PHMB’s efficacy against other pathogenic organisms, including Escherichia coli,[3] Acanthamoeba castellanii cysts and trophozoites,[5] and Nocardia asteroides.[4] A pilot study in our laboratory was performed on the ability of Staphylococcus aureus (S. aureus) to penetrate the antimicrobial gauze, and a similar trend was observed. In addition to the organisms above, it will be important to determine the efficacy of PHMB dressing in decreasing numbers of potentially infective organisms, such as other commonly isolated wound pathogens including methicillin-resistant S. aureus and Enterococcus faecalis. This study demonstrates that the gauze dressing containing an antimicrobial not only provides a barrier to P. aeruginosa but also inhibits the growth of bacteria within the dressing, thus protecting the wound and potential spread of bacteria from the dressed site. The normal flora (total bacteria) persisted in the wounded area as expected. This is an important point to consider, since reducing the normal flora of wounds may clinically increase the potential for invading pathogenic bacteria to survive. Evaluation of the use of this dressing as a protective defense mechanism to pathogenic bacteria in a clinical setting will confirm these preclinical findings and support the use of this new approach for protecting wounds from the environment. *Kerlix® A.M.D. Gauze Dressing (Kendall, a division of Tyco Healthcare Group LP, Mansfield, Massachusetts) **Kerlix® Gauze Dressing (Kendall, a division of Tyco Healthcare Group LP, Mansfield, Massachusetts)