Bacterial growth kinetic without the influence of the immune system using vacuum-assisted closure dressing with and without negative pressure in an in vitro wound model

The physical capacity of negative pressure wound therapy (NPWT) dressing on the bacterial growth in an in vitro wound model was investigated. Standardised wounds were contaminated with a clinical Staphylococcus aureus strain and incubated at 35 degrees C for 6 hours. Four wounds were treated with continuous negative pressure (125 mmHg) and four controls without. Bacterial load per gram tissue and per gram polyurethane sponge were measured after 24, 36 and 72 hours. Without negative pressure, the initial mean S. aureus load per gram tissue was 1.42 x 10(4), with negative pressure 1.84 x 10(4), P = 0.294. After 24, 36 and 72 hours, both models yielded comparable numbers of organisms (24 hours: P = 0.081; 48 hours: P = 0.455; 72 hours: P = 0.825, respectively). Bacterial load of sponges with or without negative pressure also did not differ. Over a period of 72 hours, sponges with negative pressure yielded 1.60 x 10(8), those without negative pressure yielded 1.74 x 10(8) CFU/g sponge (P = 0.876). In non vital tissue without the influence of the immune system, the bacterial load did not decrease in our in vitro model using an NPWT dressing. This observation was independent of the physical effect of continuous negative pressure at 125 mmHg. The reduction in bacteria demonstrated in previous studies appears to be caused by other effects than physical suction alone. However, the results obtained are limited as non viable tissue was used and the effect of suction on dead tissue might be very different from that occurring on perfused tissue, for example, in an animal model or in patients.

Comparison of bacteria-retaining ability of absorbent wound dressings

Fibrous materials in some modern absorbent wound dressings have the ability to sequester and retain bacteria; however, this ability varies according to the nature of the fibres. We studied the bacterial retention capacity of alginate and carboxymethylcellulose dressings, using an infected skin ulcer model on the backs of rats. Wound surfaces were inoculated with either Staphylococcus aureus or Pseudomonas aeruginosa at a concentration of 1.5 x 10(6) colony-forming units per wound. AQUACEL; Hydrofiber;, Kaltostat; or Sorbsan; were applied to the contaminated wounds for 12 h. Each dressing was then divided into two pieces. Total viable bacterial count within the dressing was calculated using one piece, and bacterial count released from the dressing into physiological saline was determined using the other piece, enabling bacterial retention rate to be calculated. Bacterial counts in tissue were also determined. Each dressing was tested on each of 10 wounds contaminated with each bacterium. Statistical analyses were performed using one-way analysis of variance (ANOVA) for replicated measures combined with Duncan's multiple comparison test. AQUACEL; Hydrofiber; dressing was most effective in its ability to retain both Staphylococcus aureus and Pseudomonas aeruginosa (p < 0.05). Bacterial counts in tissue showed no significant change with respect to pathogen or the type of dressing used. It can be concluded that the bacterial retaining ability of AQUACEL; Hydrofiber; dressing was found to be significantly higher than that of alginate dressings in an infected animal wound model.

Bacterial and fungal absorption properties of a hydrogel dressing with a superabsorbent polymer core

OBJECTIVE

To study in vitro the micro-organism absorption properties of a hydrogel wound dressing, TenderWet.

METHOD

Microbial films on agar plates and suspensions with common wound bacteria (Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa) and a fungal strain (Candida albicans) were studied.

RESULTS

The hydrogel dressing reduced the number of micro-organisms significantly, both on the agar plate and in suspension. The in vitro data show that the hydrogel dressing absorbed the micro-organisms from the environment. Electron microscopic imaging clearly demonstrated that the germs were attached to the surface of the dressing's superabsorbent polymer core.

CONCLUSION

In vitro data show that the hydrogel dressing TenderWet attracts and retains micro-organisms and reduces the number of viable germs. Clinical experience underlines this fast cleansing and debriding effect of the hydrogel wound dressing.

Evaluation of a flexible new liquid polymer wound dressing

Occlusive dressings are the foundation of wound care and have been shown to speed epithelialization and healing of surgical sites. Many different dressings have been introduced over the years including antibacterial ointments with gauze and adhesive, hydrocolloid bandages, and liquid adhesives. All of these have their limitations and advantages. We introduce our experience with a new organic polymer in solvent which when applied to a wound forms a flexible occlusive bandage. The material has been shown to have antimicrobial properties and be well-tolerated by patients.

Bacterial load in relation to vacuum-assisted closure wound therapy: a prospective randomized trial

Vacuum-assisted closure has become a new technique in the challenging management of contaminated, acute, and chronic wounds. Although promising clinical results have been described, scientific proof to substantiate the mechanism of action of this therapy is scarce. In the present study, we examined whether the positive effect on wound healing found in vacuum-assisted closure-treated wounds could be explained by an effect on the bacterial load. Fifty-four patients who needed open wound management before surgical closure were included in this study. Wounds were randomized to either vacuum-assisted closure therapy (n= 29) or treatment by conventional moist gauze therapy (n= 25). Healing was characterized by development of a clean granulating wound bed ("ready for surgical therapy") and reduction of wound surface area. To quantify bacterial load, biopsies were collected. No significant difference was found in time needed to reach "ready for surgical therapy" comparing both therapies. Wound surface area reduction was significantly larger in vacuum-assisted closure-treated wounds: 3.8 +/- 0.5 percent/day (mean +/- SEM) compared to conventional-treated wounds (1.7 +/- 0.6 percent/day; p < 0.05). The total quantitative bacterial load was generally stable in both therapies. However, nonfermentative gram negative bacilli showed a significant decrease in vacuum-assisted closure-treated wounds (p < 0.05), whereas Staphylococcus aureus showed a significant increase in vacuum-assisted closure-treated wounds (p < 0.05). In conclusion, this study shows a positive effect of vacuum-assisted closure therapy on wound healing, expressed as a significant reduction of wound surface area. However, this could not be explained by a significant quantitative reduction of the bacterial load.

In-vitro analysis for microbial barrier properties of 2-octyl cyanoacrylate-derived wound treatment films

BACKGROUND

In recent years, 2-octyl cyanoacrylate monomer has been formulated for various wound care products that have been approved by the Food and Drug Administration (FDA).

PURPOSE

To evaluate the in vitro effectiveness of 2-octyl cyanoacrylate formulation-based films as barriers to various pathogens, including bacteria, fungi, and yeast.

METHODS

The barrier properties of the cyanoacrylate films prepared by the following two methods were tested: (1) prepolymerized film and (2) in situ polymerized film. The upper surface of films was inoculated such that the microorganisms would have to penetrate the film to colonize the media beneath. Nine different organisms were used. Plates were observed for growth at two, four, and seven days after inoculation.

RESULTS

No growth was observed in any test, with the exception of prepolymerized film challenged with Pseudomonas aeruginosa. The pattern of growth observed suggests that the bacteria colonized the medium by traveling around and not through the film.

CONCLUSIONS

2-Octyl cyanoacrylate-based films are excellent microbial barriers.

Barrier and antibacterial properties of 2-octyl cyanoacrylate-derived wound treatment films

BACKGROUND

Besides enhancing healing, an ideal dressing should prevent invasion of pathogens and control the number of bacteria already present in the wounds.

OBJECTIVE

To evaluate the barrier and antimicrobial properties of a cyanoacrylate-based bandage (LAB) against Staphylococcus aureus or Pseudomonas aeruginosa on partial thickness wounds in swine.

METHODS

Barrier study: Bacteria were inoculated over test materials (LAB, standard bandage, air-exposed) that were placed over wounds. The bacteria from wounds were quantitated at 24, 48, and 72 hours postinoculation. Antimicrobial study: Wounds inoculated with bacteria were covered with LAB, standard bandage, or hydrocolloid bandage or left air-exposed. The bacteria recovered from wounds were quantitated at 24 and 72 hours after treatment.

RESULTS

Barrier study: No bacteria were recovered from LAB-treated wounds. Antimicrobial study: LAB reduced the number of inoculated bacteria in comparison to all other groups.

CONCLUSION

LAB is effective in protecting wounds from external bacterial invasion and reducing bacterial contamination.

Microbial contamination of water-soaked cotton gauze and its cause

Seven in-use cotton gauze samples and three cotton balls soaked in sterile distilled water in canisters were investigated 7 days after they were prepared in hospital. All samples were contaminated with bacteria including 10(6) to 10(7) colony forming units/ml of Pseudomonas aeruginosa. In vitro viability tests using cotton gauze and cotton balls soaked in sterile distilled water revealed rapid proliferation of P. aeruginosa, Serratia marcescens and Candida albicans. Since the cotton gauze and the cotton balls were soaked in water containing nutrients, such as protein and glucose, these materials may be readily contaminated with bacteria including P. aeruginosa. Thus, when using cotton gauze and cotton balls containing water, microbial contamination should be expected.

Human immunodeficiency virus-related primary cutaneous aspergillosis

A 31-year-old Caucasian man with AIDS developed a crusted violaceous plaque under adhesive tape near a central venous catheter insertion site. Histological examination demonstrated a ruptured hair follicle containing collections of fungal hyphae typical of Aspergillus spp. A culture of the biopsy material grew Aspergillus fumigatus. The patient responded to removal of the catheter and the occlusive dressing, in addition to itraconazole therapy. Aspergillosis must be considered in the differential diagnosis of cutaneous lesions in human immunodeficiency virus-infected patients, in particular when the lesion occurs under adhesive tape or an occlusive dressing.

Aerobic, anaerobic and fungal burn wound infections

One hundred and twenty-seven patients were studied prospectively for aerobic, anaerobic and fungal burn wound infections. All cases yielded organisms on culture. A total of 377 isolates were recovered (239 aerobes, 116 anaerobes and 22 fungi). Aerobic bacteria alone were present in 49 patients (38.6%). Anaerobic bacteria alone were present in four patients (3.2%). Candida sp. alone was present in one patient (0.8%). Mixed aerobic and/or anaerobic bacteria and/or fungi were present in 73 patients (57.5%). Fungi were isolated from 21 patients (23.9%) of 88 patients having fungal cultures. The predominant isolates recovered in descending order of frequency were: Pseudomonas aeruginosa, Staphylococcus aureus, Bacteroides sp., Klebsiella sp. and Peptostreptococcus sp. There were 70 patients (55.1%) infected with anaerobic bacteria. The rate of recovery of anaerobes was higher in patients with open wound dressing (72.7%) than in patients with occlusive wound dressings (41.7%), (P < 0.01). Seventeen patients presented with septic shock, 15 of them (88.2%) yielding positive anaerobic cultures. Bacteroides sp. were isolated from 14 patients with septic shock, and were recovered from the four patients who had anaerobic infection alone. These results indicate a significant role of Bacteroides sp. in burn wound sepsis.