Efficacy of Topical Antimicrobial Agents Against Bacterial Isolates From Burn Wounds.

Topically applied antimicrobials are key to the prevention of infection and mortality in the acute burn population. The purpose of this study was to determine the in vitro effectiveness of commercially available topical antimicrobials, as well as topical preparations that were compounded in our burn care institution. One-hundred twenty microorganisms were tested against these topical antimicrobials and in vitro effectiveness was observed. Results showed that compounded preparations of 1:1:1 + Double Antibiotic (1 part bacitracin: 1 part silver sulfadiazine: 100,000 units/g nystatin + 5 mg/g neomycin sulfate + 500 units/g polymyxin B) and 3:1 + Double Antibiotic (3 part bacitracin: 1 part silver sulfadiazine + 5mg/g neomycin sulfate + 500 units/g polymyxin B) were effective against 100% of the isolates tested. Other topical agents showed moderate effectiveness, thus demonstrating the need for multiple topical agents to reach a broad spectrum of microorganisms. However, the development of topical antimicrobial resistance needs further study.

Trends in bacterial wound isolates and antimicrobial susceptibility in a pediatric burn hospital.

The purpose of this retrospective study was to collate data dealing with organisms cultured from the burn patients and evaluate trends in antimicrobial susceptibility. All cultures collected from each acute admission patient between 2004 and 2011 in the 30-bed pediatric burn hospital were evaluated for their annual frequency and antimicrobial susceptibility. Duplicate cultures were excluded. Staphylococcus aureus was isolated most frequently (25% of total isolates; range, 69-408 isolates/yr), followed by Pseudomonas aeruginosa (13%; range, 40-202 isolates/yr), coagulase-negative staphylococci (9%; range, 2-188 isolates/yr), Enterobacter cloacae (8%; range, 22-128 isolates/yr), and Escherichia coli (6%; range, 19-91 isolates/yr). This rank order remained relatively consistent during the period of study. The emergence of methicillin-resistant S. aureus increased from 20% in 2004 to about 45% in 2009 to 2011. Susceptibility to vancomycin was still 100%. In comparing periods 2004 to 2007 and 2008 to 2011, P. aeruginosa showed increased susceptibility to cefepime (from 76% to 84%) and the aminoglycosides (from 68% to 81%), whereas susceptibility to piperacillin-tazobactam remained high (from 91% to 93%). E. cloacae demonstrated 90 to 100% susceptibility to aminoglycosides, cefepime, and imipenem. E. coli showed an increased rate of resistance to ceftazidime but was still susceptible to imipenem and amikacin. S. aureus and P. aeruginosa continue to be the most prevalent organisms cultured from our pediatric burn population. Almost half of the staphylococcal isolates were methicillin-resistant S. aureus. Despite widespread use of piperacillin-tazobactam, P. aeruginosa susceptibility remained high. Several classes of antimicrobials continued to demonstrate good to excellent activity against the majority of organisms cultured from the burn patients.

Amish burn ointment and burdock leaf dressings: assessments of antimicrobial and cytotoxic activities.

Amish burn wound ointment (ABO) contains honey, lanolin, oils, glycerin, bees wax, and other natural additives. Although there are many anecdotal reports that this ointment covered with a burdock leaf (BL) dressing promotes burn wound healing, little scientific testing of this treatment has occurred. The goal of this study was to evaluate in vitro some of the components of this treatment modality for antimicrobial and cytotoxic activities. The ABO was tested for sterility using standard microbiological techniques. Because of the semisolid, lipid-based nature of the salve, the at-use product could not be tested in bioassays. Samples of BL and the dry ingredients (DI) used in the ointment were provided by the Amish vendor. Aqueous extracts of the DI and of the BL were prepared and freeze dried. The freeze-dried extracts were reconstituted, filtered, and tested separately on keratinocyte and fibroblast cell cultures for cytotoxicity (growth inhibition assay) and against a panel of susceptible and resistant microbes for antimicrobial activity (Nathan's agar-well diffusion assay) in a series of concentrations (% wt/vol). Neither DI nor BL extracts demonstrated antimicrobial activity against any of organisms tested. The DI extract inhibited growth of both keratinocytes and fibroblasts at the 0.1% concentration. The 0.1 and 0.03% concentrations of the BL extract were cytotoxic to both keratinocytes and fibroblasts. Although tests for microbial growth from the at-use preparation of the ABO were negative, extracts of the DI and BL did not demonstrate any antimicrobial activity. Additionally, both extracts inhibited the growth of skin cells in vitro at higher concentrations. These results suggest caution in the use of ABO and BL dressings if there is more than a minimal risk of complications from the burn injury.

Pharmacokinetics of colistin in an adolescent boy with extensive burn injury.

Multidrug resistance in Gram-negative bacteria has led to a resurgence in colistin use. No pharmacokinetic data exist for burn patients. A 17-year-old boy suffered a 71% TBSA full-thickness burn with deep necrosis and compartment syndrome. He developed multidrug-resistant Acinetobacter baumannii burn wound sepsis/septic shock with acute renal failure requiring dialysis. The organism was resistant to all tested antibiotics except colistin. He received colistin 2.5 mg/kg every 24 hours. Peak and trough serum concentrations, area under the concentration-time curve, and elimination half-lives of colistin were 3.6 ± 1.0 µg/ml, 0.9 ± 0.5 µg/ml, 47.1 ± 14.4 mg · hr/L, and 12.3 ± 9.4 hours (mean ± SD), respectively. Serum levels were at or above the minimum inhibitory concentration for >90% of therapy. Nevertheless, salvage therapy with colistin proved futile as the patient developed acidosis, coagulopathy, and was vasopressor-dependent without any wound healing. He died on hospital day 52. Microbiologically, the serum levels of colistin were seemingly adequate, as repeat cultures were negative. Given the peak and trough levels of colistin relative to the minimum inhibitory concentration for the organism (0.5 µg/ml), it would seem that the dosage of 2.5 mg/kg administered every 24 hours for this patient on dialysis was appropriate. Patients on dialysis infected with an organism possessing a higher inhibitory concentration (≥1 µg/ml) should probably receive the same dosage every 12 hours to avoid subtherapeutic concentrations. Large-scale study of the pharmacokinetics of colistin in patients with burn injury is urgently needed.

Are topical antimicrobials effective against bacteria that are highly resistant to systemic antibiotics?

An increasing number of bacteria are resistant to multiple systemic antibiotics. The purpose of this study was to determine if topical antimicrobials are still effective against multi-drug resistant organisms (MDROs). MDROs, including Acinetobacter, Pseudomonas, Klebsiella, Staphylococcus, and Enterococcus, were collected from four burn hospitals. The sensitivity of 47 MDROs to 11 commonly used topical agents (mafenide acetate, nystatin, mafenide + nystatin, silver nitrate, Dakin's, polymyxin B, neomycin, polymyxin + neomycin, silver sulfadiazine, bacitracin, silver sulfadiazine + bacitracin) was tested using the agar well diffusion assay and compared with the sensitivity of 27 non-MDROs of similar genera. Overall 88% of the tests of the non-MDROs showed susceptibility to the topicals compared with 80% for the MDROs (P < .05). Specific findings included: all of the gram-positive non-MDROs were sensitive to bacitracin compared with only 67% of the MDROs (P < .05); 74% of the non-MDROs were sensitive to neomycin vs 26% of the MDROs (P < .01). Even for the susceptible isolates, the zones of inhibition were smaller for the MDROs than for the non-MDROs (P < .002), indicating decreased susceptibility of the MDROs. Specifically, while the MDRO Acinetobacter were sensitive to most of the topicals, the zones of inhibition for silvadene, silvadene + bacitracin, neomycin, and neomycin + polymyxin were significantly smaller (P < .001) for the Acinetobacter MDROs than the non-MDROs. Although many topicals are still effective against some MDROs, MDROs are more resistant to topicals than are non-MDROs. Some treatment assumptions based historically on the efficacy of topical antimicrobial agents against non-MDROs need to be re-evaluated for MDROs.

Assessment of a silver-coated barrier dressing for potential use with skin grafts on excised burns.

Acticoat burn dressing is a silver-coated dressing with antimicrobial activity purported to reduce infection from environmental organisms in partial and full-thickness wounds. Acticoat was tested for activity as an antimicrobial treatment and as an antimicrobial barrier dressing in three in vitro assays. It was found that a modified disc assay method gave false negative results but in an assay in which bacteria were inoculated on top of samples of Acticoat, bacterial numbers were reduced, over time, with all microorganisms tested. Acticoat served as a barrier for bacteria, inoculated onto it, from contaminating the surface of an agar plate under the Acticoat. The data show that Acticoat has: antimicrobial capabilities, but to be effective hours of contact between Acticoat and the microorganisms are required; and the capacity to serve as an antimicrobial barrier dressing. These findings support the conclusion that Acticoat has activity to reduce microbial contamination of wounds from environmental sources.