Multiple in vitro models were utilised to evaluate the biofilm management capabilities of seven commercially‐available wound dressings, varying in composition and antibacterial ingredients, to reduce common aerobic, anaerobic, and multispecies biofilms. The Center for Disease Control bioreactor was used to evaluate single species Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) 24 and 48 hours biofilms, as well as a multispecies biofilm consisting of these two organisms in addition to Enterococcus faecalis (E. faecalis). As wound biofilms often exist in hypoxic wound environments, a direct contact anaerobic model system was used to evaluate efficacy on Bacteroides fragilis (B. fragilis). Biofilm control was evaluated against P. aeruginosa in the drip flow bioreactor model, where a constant flow of proteinaceous media is used to create a more challenging and wound‐like model. The results demonstrated that biofilm management capabilities varied amongst wound dressings. Two dressings, a controlled‐release iodine foam dressing and a silver nanocrystalline dressing, showed potent >4 log reductions in recovered organisms compared with untreated controls in all biofilm models evaluated. The effectiveness of other dressings to manage bioburden varied between dressing, test organism, and model system. A silver foam dressing showed moderate biofilm control in some models. However, biofilm exposure to methylene blue and gentian violet‐containing foam dressings showed negligible log reductions in all in vitro biofilm methods examined. The data outlined in this in vitro study support the use of the iodine foam dressing for wounds with infection and biofilm.

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Treatment of chronic wounds that are at risk of infection, or that are infected, require the use of antimicrobial dressings, most often those that contain silver. Silver exerts its antimicrobial effects by binding to multiple cellular components and, as such, bacterial resistance to it is low; however, molecular silver resistance has been documented and is attributed to the presence of the sil operon or changes in genes encoding porin and efflux pump expression. The aim of this study was to evaluate spontaneous silver resistance development in common opportunistic pathogens, Staphylococcus, Pseudomonas and Enterococcus cloacae, as well as resistance development when exposed to subtherapeutic concentrations over a prolonged period. Furthermore, following silver resistance development, cross-resistance to several classes of antibiotics was evaluated. Following exposure of the strains to silver sulfadiazine (SSD) at two times and four times minimum inhibitory concentration (MIC), the mutation rate was <1010 colony forming unit (CFU)/mL. Serial passage of S. aureus and P. aeruginosa in subinhibitory concentrations of SSD selected for no resistant mutants. The SSD MIC of E. cloacae increased past the solubility limit of SSD at serial passage 17. MIC testing of this isolate showed a >2048-fold increase in MIC to silver in comparison to the parent strain. MIC testing of the serial passage isolates demonstrated no cross-resistance to antibiotics from six different classes. Overall, the results of this study show resistance development to silver is low and, if it does occur, it does not confer resistance to several antibiotic classes. However, as this study was carried out with a small number of strains, a study with a larger panel of strains and sequencing of the strains to determine the exact mechanism of resistance would be needed to investigate the threat of silver resistance further.

This study evaluated the antimicrobial and antibiofilm activity of a concentrated surfactant gel preserved with antimicrobials and a concentrated surfactant gel with 1% silver sulfadiazine (SSD) against 12 clinical strains of Acinetobacter baumannii and the type strain A. baumannii ATCC 19606. Approach: The biofilm-forming potential of the A. baumannii isolates was investigated using a crystal violet assay and classifying the isolates as ''nonadherent,'' ''weak,'' ''moderate,'' or ''strong'' biofilm formers. The antimicrobial activity was determined using the zone of inhibition (ZOI) method. The antibiofilm activity was evaluated against A. baumannii ATCC 19606 using the Center for Disease Control bioreactor model. Results: A. baumannii readily forms biofilms with 8 out of the 12 clinical isolates being classified as strong biofilm formers (OD 570 > 0.4). The concentrated surfactant gel with 1% SSD demonstrated antimicrobial activity against all isolates with a ZOI of 7.2-14 mm. Antibiofilm activity against a 24 h biofilm of A. baumannii ATCC 19606 was found, with a ‡7 log decrease in bacterial cell density following 24 h treatment with the concentrated surfactant gel with 1% SSD. The concentrated surfactant gel preserved with antimicrobials also showed some biofilm disruption with *3 log decrease in bacterial cell density being found. Innovation: The concentrated surfactant gel with 1% SSD used in this study showed antimicrobial and antibiofilm activity against A. baumannii. Conclusion: The concentrated surfactant gel with 1% SSD used in this study showed efficacy against A. baumannii, a common cause of wound infections, and should be considered for treatment of wounds infected with A. baumannii in health care settings.