Effect of Bacterial Biofilms on Topical Antimicrobial Therapy

Abstract Chronic wounds are frequently complicated by bacterial biofilm formation, which significantly impairs healing and reduces the effectiveness of antimicrobial therapy. The aim of this study was to evaluate the efficacy of commonly used topical antimicrobial agents against multidrug-resistant wound pathogens in relation to the timing of their application and the stage of biofilm development. Multidrug-resistant bacterial strains isolated from non-healing wounds were used to create an experimental collection, including Pseudomonas aeruginosa , Staphylococcus aureus , Escherichia coli , Enterococcus faecalis , and Acinetobacter baumannii . Biofilm formation was assessed using the microtiter plate method according to Stepanović et al. The antimicrobial efficacy of 11 topical agents in various pharmaceutical forms was subsequently tested in a modified in vitro burn wound model based on Hammond et al., with three time intervals representing different stages of biofilm development (4, 6, and 24 hours after inoculation). All tested strains demonstrated the ability to form biofilm, with a significant increase in intensity over time. In the early stages (4–6 hours), several agents, including octenidine-, iodine-, and silver-based preparations, exhibited strong bactericidal activity across most strains. However, when treatment was delayed to 24 hours, corresponding to mature biofilm formation, the efficacy of the majority of agents markedly decreased, often approaching the effect of sterile gauze. Only octenidine- and iodine-based agents retained partial activity against selected pathogens. The findings confirm that the timing of topical antimicrobial application is a key determinant of therapeutic success. Early intervention significantly enhances antimicrobial efficacy, whereas delayed treatment in the presence of established biofilm leads to substantially reduced effectiveness. These results highlight the importance of prompt and proactive wound management and support the need for multimodal strategies combining antimicrobial therapy with biofilm disruption.