Clinically isolated bacteria resistance to silver-based wound dressings.

OBJECTIVE: Silver has become a global treatment option with the US Food and Drug Administration providing marketing clearance for many silver-impregnated wound dressings and topical agents. However, the increased use of silver-based products across medical disciplines has raised questions concerning the development of acute silver resistance. In this study, the efficacy of previously identified silver-resistant clinical bacteria (Klebsiella pneumoniae and Enterobacter cloacae) against a variety of commercially available silver-based wound dressings was further investigated. METHOD: To further explore the clinical significance of these isolates, multiple time-course and repeat-challenge assays were conducted with nine dressings using a panel of silver-resistant and silver-sensitive microorganisms. Silver-impregnated dressings were ranked by silver species, quantity of silver and overall efficacy. RESULTS: Both silver-resistant strains were largely unaffected and exhibited phenotypic resistance even when exposed to the high silver concentrations found in commercially available wound dressings. In stark contrast, the majority of the dressings were able to maintain a high degree of efficacy over the course of 72 hours and during repeated bacterial challenges against silver-sensitive microorganisms. CONCLUSION: Our findings provide additional evidence that clinically significant silver-resistance has emerged in the clinical setting. Such resistant microbes are capable of sustained silver resistance against a wide variety of silver adjuvants. These findings suggest that the further development and dissemination of these resistance mechanisms could significantly impact current practices in wound healing.

Management of Tissue Loss After Agkistrodon Snakebite: Appropriate Use of Crotalidae-Fab Antivenin.

Although initially created for the treatment of rattlesnake (genus: Crotalus) bites, Crotalidae-Fab antivenin is used to treat many different pit viper envenomations. However, the efficacy of Crotalidae-Fab in preventing tissue loss from copperhead (Agkistrodon contortrix) or cottonmouth (Agkistrodon piscivorus) snakebites remains unclear. Recent reports show that Agkistrodon-related bites rarely require treatment beyond simple observation and pain control. The purpose of this study was to examine the amount of tissue loss in patients who received Crotalidae-Fab compared with those who did not after an Agkistrodon bite. After institutional review board approval, a retrospective study was completed at a Level 1 trauma center. Between 2009 and 2013, a total of 57 snakebites were identified. Of the 57 bites, the snake species was documented in 36 cases including 31 copperheads, 1 cottonmouth, and 4 rattlesnakes. The other 21 bites were from unknown or nonvenomous species. Of the 32 Agkistrodon-related bites, 15 patients received Crotalidae-Fab (average of 3 vials administered) and 17 did not receive Crotalidae-Fab. None of the 32 patients, regardless of treatment option, had tissue loss or required surgical interventions. Only 1 patient received Crotalidae-Fab and debridement of a vesicle associated with the bite. No clinically significant differences were observed between the groups. These findings support previous literature that failed to show added benefit of Crotalidae-Fab treatment for Agkistrodon bites beyond patient comfort and pain control. Evaluation of current protocols for Agkistrodon envenomations is warranted. Snakebite wound education in trauma physicians and nurses may decrease unnecessary use of antivenom medication.

Unprecedented Silver Resistance in Clinically Isolated Enterobacteriaceae: Major Implications for Burn and Wound Management.

Increased utilization of inorganic silver as an adjunctive to many medical devices has raised concerns of emergent silver resistance in clinical bacteria. Although the molecular basis for silver resistance has been previously characterized, to date, significant phenotypic expression of these genes in clinical settings is yet to be observed. Here, we identified the first strains of clinical bacteria expressing silver resistance at a level that could significantly impact wound care and the use of silver-based dressings. Screening of 859 clinical isolates confirmed 31 harbored at least 1 silver resistance gene. Despite the presence of these genes, MIC testing revealed most of the bacteria displayed little or no increase in resistance to ionic silver (200 to 300 µM Ag(+)). However, 2 isolates (Klebsiella pneumonia and Enterobacter cloacae) were capable of robust growth at exceedingly high silver concentrations, with MIC values reaching 5,500 µM Ag(+). DNA sequencing of these two strains revealed the presence of genes homologous to known genetic determinants of heavy metal resistance. Darkening of the bacteria's pigment was observed after exposure to high silver concentrations. Scanning electron microscopy images showed the presence of silver nanoparticles embedded in the extracellular polymeric substance of both isolates. This finding suggested that the isolates may neutralize ionic silver via reduction to elemental silver. Antimicrobial testing revealed both organisms to be completely resistant to many commercially available silver-impregnated burn and wound dressings. Taken together, these findings provide the first evidence of clinical bacteria capable of expressing silver resistance at levels that could significantly impact wound management.