Silver Resistance identified in clinically isolated Enterobacteriaceae: Major Implications for Burn and Wound Care

During the last 40 years, inorganic silver has become a popular additive for many medical devices including burn and wound dressings. As a result, concerns of widespread silver-resistance emerging in clinical bacteria have been raised. Previously, we identified the first clinical bacteria (Klebsiella pneumoniae and Enterobacter cloacae) capable of luxuriant growth at exceedingly high concentrations of silver. Additional DNA sequence analysis revealed PCR products from these isolates had a high degree of similarity to other plasmids containing genes which encode for heavy metal resistance. These plasmids included pKPN3, pMG101, and many megaplasmids in the Klebsiella taxid. This finding suggests the existence of many genetically similar plasmids all with potential capabilities of expressing high levels of silver-resistance. Further antimicrobial testing against commercially-available silver dressings showed after 24 hours of dynamic contact, the silver-resistant isolates were largely resistant to many of the dressings. Data from a corrected zone of inhibition (CZOI) assay supported these findings. Neither of the silver-resistant isolates produced significant zones of inhibition after contact with the dressings, while the non-resistant organisms yielded a measureable zone of inhibition. Swabs from underneath the dressing post-incubation revealed the silver-resistant bacteria remained viable. Research revealed non-silver based wound dressings maintained high antimicrobial efficacy against these clinical bacteria without the risk of resistance. The development of acute silver- resistance would have significant consequences on wound care and patient outcomes. There is a significant need for non-silver based dressings that can effectively manage bioburden while minimizing resistant risks. Due to a current lack of antimicrobial stewardship practices for silver-based treatments, continued monitoring for silver-resistance is warranted.